Drinking Water Glossary
ABC. See Association of Boards of Certification.
absorbed dose. The amount of a chemical that enters the
  body of an exposed organism.
absorption. The uptake of water or dissolved chemicals by a
  cell or an organism (as tree roots absorb dissolved nutrients
  in the soil).
absorption factor. The fraction of a chemical making contact
  with an organism that is absorbed by the organism.
acceptable daily intake (ADI). Estimate of the largest
  amount of chemical to which a person can be exposed on a
  daily basis that is not anticipated to result in adverse effects
  (usually expressed in mg/kg/day). Same as RfD.
accuracy. How closely an instrument measures the true or
  actual value of the process variable being measured or
acid mine drainage. Drainage of water from areas that have
  been mined for coal of other mineral ores; the water has
  low pH, sometimes less than 2.0 (is acid), because of its
  contact with sulfur-bearing material; acid drainage is
  harmful because it often kills aquatic organisms.
acid rain. Precipitation which has been rendered (made)
  acidic by airborne pollutants.
acidic (uh-SlD-ick). The condition of water or soil which
  contains a sufficient amount of acid substances to lower the
  pH below 7.0.
acidified (uh-SlD-uh-FIE-d). The addition of an acid
  (usually nitric or sulfuric)  to a sample to lower the pH
  below 2.0. The purpose of acidification is to "fix" a sample
  so it won't change until it is analyzed.
acre-foot. A volume of water that covers one acre to a depth
  of one foot, or 43,560 cubic feet (1233.5 cubic meters).
activated carbon. Adsorptive particles or granules of carbon
  usually obtained by heating carbon (such as wood). These
  particles or granules have  a high capacity to selectively
  remove certain trace and soluble materials from water.
active transport. An energy-expending mechanism by which
  a cell moves a chemical across the cell membrane from a
  point of lower concentration to a point of higher concentra-
  tion, against the diffusion  gradient.
action level. The concentration of lead or copper in water
  specified at Code of Federal Regulations 141.80(c) which
  determines, in some cases, the treatment requirements
  contained in subpart I of this part that a water system is
  required to complete.
acute. Occurring over a short period of time; used to describe
  brief exposures and effects which appear promptly after
acute exposure. A single exposure to a toxic substance which
  results in severe biological harm or death. Acute exposures
  are usually characterized as lasting no longer than a day.
acute toxicity. The ability of a substance to cause poisonous
  effects resulting in severe biological harm or death soon
  after a single exposure or dose. Also, any severe poisonous
  effect resulting from a single short-term exposure to a toxic
additive effect. Combined effect of two or more chemicals
  equal to the sum of their individual effects.
adsorbate (add-SORE-bait). The material being removed by
  the adsorption process.
adsorbent (add-SORE-bent). The material (activated
  carbon) that is responsible for removing the undesirable
  substance in the adsorption process.
adsorption. The process by which chemicals are held on the
  surface of a mineral or soil particle (compare with Absorp-
aeration (air-A-shun). The process of adding air to water.
  Air can be added to water by either passing air through
  water or passing water through air.
aerobic (air-O-bick). A condition in which "free" (atmo-
  spheric) or dissolved oxygen is present in the water.
age tank. A tank used to store a chemical solution of known
  concentration for feed to a chemical feeder. Also called a
  day tank.
aggregate.  A mass or cluster of soil particles, often having a
  characteristic shape.
agrochemical. Synthetic chemicals (pesticide and fertilizers)
  used in agricultural production.
air binding. A situation where air enters the filter media. Air
  is harmful to both the filtration and backwash processes. Air
  can prevent the passage of water during the filtration
  process and can cause the loss of filter media during the
  backwash process.
air gap. An open vertical drop, or vertical empty space, that
  separates a drinking (potable) water supply to be protected
  from another water system in a water treatment plant or
  other location. This open gap prevents the contamination of
  drinking water by backsiphonage or backflow because there
  is no way raw water or any other water can reach the
  drinking water.
air padding. Pumping dry air into a container to assist with
  the withdrawal of a liquid or to force a liquefied gas such as
  chlorine out of a container.
air stripping. A treatment process  used to remove dissolved
  gases and volatile substances from water. Large volumes of
  air are bubbled through the water being treated to remove
  (strip out) the dissolved gases and volatile substances. Also
  see packed tower aeration.
alarm contact. A switch that operates when some pre-set
  low, high or abnormal condition exists.
algae. Microscopic plants which contain chlorophyll and live
  floating or suspended in water. They also may be attached
  to structures, rocks or other submerged surfaces. They are

                                             Drinking Water Glossary
 food for fish and small aquatic animals. Excess algal
 growths can impart tastes and odors to potable water. Algae
 produce oxygen during sunlight hours and use oxygen
 during the night hours. Then- biological activities apprecia-
 bly affect the pH and dissolved oxygen of the water.
algal bloom (AL-gull). Sudden, massive growths of micro-
 scopic and macroscopic plant life, such as green or blue-
 green algae, which develop in lakes and reservoirs.
algicide (AL-gi-SlDE). Any substance or chemical specifi-
 cally formulated to kill or control algae.
aliphatic hydroxy acids (AL-uh-FAT-ick). Organic acids
 with carbon atoms arranged in branched or unbranched
 open chains rather than in rings.
aliquot (AL-li-kwot). Portion of a sample.
alkali (AL-ka-Iie). Various soluble salts, principally of
 sodium, potassium, magnesium, and calcium, that have the
 property of combining with acids to form neutral salts and
 may be used in chemical water treatment processes.
alkaline (AL-ka-LlNE). The condition of water or soil which
 contains a sufficient amount of alkali substances to raise the
 pH above 7.0.
alkalinity (AL-ka-LIN-it-tee). The capacity of water to
 neutralize acids. This capacity is caused by the water's
 content of carbonate, bicarbonate, hydroxide and occasion-
 ally borate, silicate, and phosphate. Alkalinity is expressed
 in milligrams per liter of equivalent calcium carbonate.
 Alkalinity is not the same as pH because water does not
 have to be strongly basic (high pH) to have a high alkalin-
  ity. Alkalinity is a measure of how much acid can be added
 to a liquid without causing a great change in pH.
alluvial (uh-LOU-vee-ul). Relating to mud and/or sand
  deposited by flowing water. Alluvial deposits may occur
  after a heavy rain storm.
alternating current (A.C.). An electric current that reverses
  its direction (positive/negative values) at regular intervals.
ambient. Environmental or surrounding conditions.
ambient temperature (AM-bee-ent). Temperature of the
  surrounding air (or other medium). For example, tempera-
  ture of the room where a gas chlorinator is installed.
ammonium. One form of nitrogen that is usable by plants.
amperage (AM-purr-age). The strength of an electric
  current measured  hi amperes. The amount of electric
  current flow, similar to the flow of water in gallons per
ampere (AM-peer). The unit used to measure current
  strength. The current produced by an electromotive force of
  one volt acting through a resistance of one ohm.
amperometric (am-PURR-o-MET-rick). Based on the
  electric current that flows between two electrodes in a
amperometric titration. A means of measuring concentra-
  tions of certain substances in water (such as strong oxidiz-
  ers) based on the electric current that flows during a
  chemical reaction. See titrate.
anaerobic (AN-air-O-bick). A condition hi which "free"
  (atmospheric) or dissolved oxygen is NOT present in water.
analog. The readout of an instrument by a pointer (or other
  indicating means) against a dial or scale.
analyzer. A device which conducts periodic or continuous
  measurement of some factor such as chlorine, fluoride or
  turbidity. Analyzers operate by any of several methods
  including photocells, conductivity or complex instrumenta-
animal studies. Investigations using animals as surrogates for
  humans, on the expectation that results in animals are
  pertinent to humans.
anion (AN-EYE-en). A negatively charged ion in an
  electrolyte solution, attracted to the anode under the
  influence of a difference in electrical potential. Chloride
  (C1-) is an anion.
anionic polymer (AN-eye-ON-ick). A polymer having
  negatively charged groups of ions; often used as a filter aid
  and for dewatering sludges.
annular space (AN-you-ler). A ring-shaped space located
  between two circular objects, such as two pipes.
anode (an-O-d). The positive pole or electrode of an electro-
  lytic system, such as a battery. The anode attracts nega-
  tively charged particles or ions (anions).
antagonism. Interference or inhibition of the effect of one
  chemical by  the action of another chemical.
appropriative. Water rights to or ownership of a water
  supply which is acquired for the beneficial use of water by
  following a specific legal procedure.
appurtenance (uh-PURR-ten-nans). Machinery, appliances,
  structures and other parts of the main structure necessary to
  allow it to operate as intended, but not considered part of
  the main structure.
aquatic. Plants of animal life living in, growing in, or
  adapted to water.
aqueous (A-kwee-us). Something made up of, similar to, or
  containing water; watery.
aquifer (ACK-wi-fer). A natural underground layer of
  porous, water-bearing materials (sand, gravel) usually
  capable of yielding a large amount or supply of water.
artesian (are-TEE-zhun - aquifer or well). Water held
  under pressure in porous rock or soil confined by imperme-
  able geologic formations. An artesian well is free flowing.
  See confined aquifer.
 aseptic (a-SEP-tick). Free from the living germs of disease,
  fermentation or putrefaction.  Sterile.
 assay. A test for a particular chemical or effect.
 Association of Boards of Certification. An international
  organization representing over 150 boards which certify the
  operators of waterworks and waste water facilities. For
  information on ABC publications regarding the preparation

                                             Drinking Water Glossary
  of and how to study for operator certification examinations,
  contact ABC, 4261/2 Fifth Street, P.O. Box 786, Ames,
  Iowa 50010-0786.
asymmetric (A-see-MET-rick). Not similar in size, shape,
  form or arrangement of parts on opposite sides of a line,
  point or plane.
atom. The smallest unit of a chemical element; composed of
  protons, neutrons and electrons.
available chlorine. A measure of the amount of chlorine
  available in chlorinated lime, hypochlorite compounds, and
  other materials that are used as a source of chlorine when
  compared with that of elemental (liquid or gaseous)
available expansion. The vertical distance from the sand
  surface to the underside of a trough in a sand filter. This
  distance is also called FREEBOARD.
axial to impeller. The direction in which material being
  pumped flows around the impeller or flow parallel to the
  impeller shaft.
axis of impeller. An imaginary line running along the center
  of a shaft (such as an impeller shaft).


back pressure. A pressure that can cause water to backflow
  into the water supply when a user's water system is at a
  higher pressure than the public water system.
backflow. A reverse flow condition, created by a difference
  in water pressures, which causes water to flow back into the
  distribution pipes of a potable water supply from any source
  or sources  other than an intended source. Also see backsi-
  phonage and cross-connection.
background level. In toxic substances monitoring, the
  average presence of a substance in the environment,
  originally referring to naturally occurring phenomena.
backsiphonage. A form of backflow caused by a negative or
  below atmospheric pressure within a water system. Also see
  backflow and cross-connection.
backwashing. The process of reversing the flow of water
  back through the filter media to remove the entrapped
bacteria (back-TEER-e-uh). Singular: bacterium. Micro-
  scopic living organisms usually consisting of a single cell.
  Bacteria can aid hi pollution control by consuming or
  breaking down organic matter in sewage, or by similarly
  acting on oil spills or other water pollutants. Some bacteria
  in soil, water or  air may also cause human, animal and plant
  health problems.
baffle. A flat board or plate, deflector, guide or similar device
  constructed or placed in flowing water or slurry systems to
  cause more uniform flow velocities, to absorb energy, and
  to divert, guide, or agitate liquids (water, chemical solu-
  tions, slurry).
bailer (BAY-ler). A 10- to 20-foot-long pipe equipped with a
  valve at the lower end. A bailer is used to remove slurry
  from the bottom or the side of a well as it is being drilled.
base metal. A metal (such as iron) which reacts with dilute
  hydrochloric acid to form hydrogen. Also see noble metal.
batch process. A treatment process in which a tank or reactor
  is filled, the water is treated or a chemical solution is
  prepared, and the tank is emptied. The tank may then be
  filled and the process repeated.
best available technology (BAT). The best technology
  treatment techniques, or other means which the Administra-
  tor finds, after examination for efficacy under field condi-
  tions and not solely under laboratory conditions, are
  available (taking cost into consideration). For the purposes
  of setting MCLs for synthetic organic chemicals, any BAT
  must be at least as effective as granular activated carbon.
best management practices (BMPs). Structural,
  nonstructural and managerial techniques that are recognized
  to be the most effective and practical means to control
  nonpoint source pollutants yet are compatible with the
  productive use of the resource to which they are applied.
  BMPs are used in both urban and agricultural areas.
bias. An inadequacy in experimental design that leads to
  results or conclusions not representative of the population
  under study.
bioaccumulation. The retention and concentration of a
  substance by an organism.
bioassay. Test which determines the effect of a chemical on a
  living organism.
biochemical oxygen demand (BOD). The amount of oxygen
  consumed by microorganisms (mainly bacteria) and by
  chemical reactions in the biodegradation of organic matter.
bioconcentration. The accumulation of a chemical hi tissues
  of an organism (such as fish) to levels that are greater than
  the level hi the medium (such as water) in which the
  organism resides (see bioaccumulation).
biodegradation. Decomposition of a substance into more
  elementary compounds by the action of microorganisms
  such as bacteria.
biological growth. The activity and growth of any and all
  living organisms.
bio remediation. A  process of adding nutrient to ground
  water to speed up the natural process in which bacteria
  break down gasoline into harmless compounds.
biotransformation. Conversion of a substance into other
  compounds by organisms; includes biodegradation.
black water. Liquid and solid human body waste and the
  carriage water generated through toilet usage.
blank. A bottle containing only dilution water or distilled
  water; the sample being tested is not added. Tests are
  frequently run on a SAMPLE and a BLANK and the
  differences are compared.
BOD. See biochemical oxygen demand.

                                             Drinking Water Glossary
bonnet (BON-it). The cover on a gate valve.
brackish. Mixed fresh and salt waters.
brake horsepower. 1) The horsepower required at the top or
  end of a pump shaft (input to a pump). 2) The energy
  provided by a motor or other power source.
breakpoint chlorination. Addition of chlorine to water until
  the chlorine demand has been satisfied. At this point,
  further additions of chlorine will result in a free residual
  chlorine that is directly proportional to the amount of
  chlorine added beyond the breakpoint.
breakthrough. A crack or break in a filter bed allowing the
  passage of floe or particulate matter through a filter. This
  will cause an increase in filter effluent turbidity. A break-
  through can occur: 1) when a filter is first placed in service,
  2) when the effluent valve suddenly opens or closes, and 3)
  during periods of excessive head loss through the filter
  (including when the filter is exposed to negative heads).
brinelling (bruh-NEL-ing). Tiny indentations (dents) high
  on the shoulder of the bearing race or bearing. A type of
  bearing failure.
buffer. A solution or liquid whose chemical makeup neutral-
  izes acids or bases without a great change in pH.
buffer capacity. A measure of the capacity of a solution or
  liquid to neutralize acids or bases. Tis is a measure of the
  capacity of water for offering a resistance to changes in pH.
buffer strips. Strips of grass or other close-growing vegeta-
  tion that separate a waterway (ditch, stream, creek) from an
  intensive land use area (subdivision, farm); also referred to
  as filter strips, vegetated filter strips, and grassed buffers.
bw. Body weight
C factor. A factor or value used to indicate the smoothness of
  the interior of a pipe. The higher the C Factor, the smoother
  the pipe, the greater the carrying capacity, and the smaller
  the friction or energy losses from water flowing in the pipe.
  To calculate the C Factor, measure the flow, pipe diameter,
  distance between two pressure gages, and the friction or
  energy loss of the water between the gages.
C Factor = Flow (GPM)/193. 75 (Diameter, ft)*63 (Slope)0 54

caisson (KAY-sawn). A structure or chamber which is
  usually sunk or lowered by digging from the inside. Used to
  gain access to the bottom of a stream or other body of
CAG. Carcinogen Assessment Group.
calcium carbonate (CaCO.,) equivalent An expression of
  the concentration of specified constituents in water in terms
  of their equivalent value to calcium carbonate. For example,
  the hardness in water which is caused by calcium, magne-
  sium and other ions is usually described as calcium carbon-
  ate equivalent.
calibration. A procedure which checks or adjusts an
  instrument's accuracy by comparison with a standard or
cancer. A disease characterized by the rapid and uncontrolled
  growth of aberrant cells into malignant tumors.
capillary action. The movement of water through very small
  spaces due to molecular forces.
capillary forces. The molecular forces which cause the
  movement of water through very small spaces.
capillary fringe. The porous material just above the water
  table which may hold water by capillarity (a property of
  surface tension that draws water upwards) in the smaller
  void spaces.
capital costs. Costs (usually long-term debt) of financing
  construction and equipment. Capital costs are  usually fixed,
  one-time expenses which are independent of the amount of
  water produced.
carcinogen (car-SIN-o-jen). Any substance which tends to
  produce cancer in an organism.
carcinogenic. Cancer-producing.
CAS registration number. A number assigned by the
  Chemical Abstracts  Service to identify a chemical.
catalyst (CAT-uh-LIST). A substance that changes the speed
  or yield of a chemical reaction without being consumed or
  chemically changed by the chemical reaction.
catalyze (CAT-uh-LIZE). To act as a catalyst. Or, to speed
  up a chemical reaction.
catalyzed (CAT-uh-LlZED). To be acted upon by a catalyst.
cathode (KA-thow-d). The negative pole or electrode of an
  electrolytic cell or system.  The cathode attracts positively
  charged particles or ions (cations).
cathodic protection (ca-THOD-ick). An electrical system
  for prevention of rust, corrosion, and pitting of metal
  surfaces which are in contact with water or soil. A low-
  voltage current is  made to flow through a liquid (water) or a
  soil in contact with the metal in such a manner that the
  external electromotive force renders the metal structure
  cathodic. This concentrates corrosion on auxiliary anodic
  parts which are deliberately allowed to corrode instead of
  letting the structure  corrode.
cation (CAT-EYE-en). A positively charged ion in an
  electrolyte solution, attracted to the cathode under the
  influence of a difference in electrical potential. Sodium ion
  (Na+) is a cation.
cationic polymer. A polymer having positively charged
  groups of ions; often used as a coagulant aid.
cavitation (CAV-uh-TAY-shun). The formation and
  collapse of a gas pocket or bubble  on the blade of an
  impeller or the gate of a valve. The collapse of this gas
  pocket or bubble drives water into the impeller or gate with
  a terrific force that can cause pitting on the impeller or gate

                                             Drinking Water Glossary
  surface. Cavitation is accompanied by loud noises that
  sound like someone is pounding on the impeller or gate
  with a hammer.
central nervous system. Portion of the nervous system
  which consists of the brain and spinal cord; CNS.
centrate. The water leaving a centrifugal after most of the
  solids have been removed.
centrifugal pump (sen-TRlF-h-gull). A pump consisting of
  an impeller fixed on a rotating shaft that is enclosed in a
  casing, and having an inlet and discharge connection. As the
  rotating impeller whirls the water around, centrifugal force
  builds up enough pressure to force the water through the
  discharge outlet.
centrifuge. A mechanical device that uses centrifugal or
  rotational forces to separate solids from liquids.
check valve. A special valve with a hinged disc or flap that
  opens in the direction of normal flow and is forced shut
  when flows attempt to go in the reverse or opposite direc-
  tion of normal flow.
chelation (key-LAY-shun). A chemical complexing (form-
  ing or joining together) of metallic cations (such as copper)
  with certain organic compounds, such as EDTA (ethylene
  diamine tetracetic acid). Chelation is used to prevent the
  precipitation of metals (copper). Also see sequestration.
chemical oxygen demand (COD). An indirect measure of
  the amount of oxygen used by inorganic and organic matter
  in water.  The measure is a laboratory test based on a
  chemical oxidant and therefore does not necessarily
  correlate with biochemical, oxygen demand.
chisel plowing. Cropland preparation by a special implement
  (chisel) that avoids complete inversion of the soil (as occurs
  with conventional moldboard plowing). Chisel plowing can
  leave a protective cover of crop residues on the soil surface
  that helps prevent erosion and improve infiltration.
chloramines (KLOR-uh-means). Compounds formed by the
  reaction of hypochlorous acid (or aqueous chlorine) with
chlorination (KLOR-uh-NAY-shun). The application of
  chlorine to water, generally for the purpose of disinfection,
  but frequently for accomplishing other biological or
  chemical results (aiding coagulation and controlling tastes
  and odors).
chlorinator (KLOR-uh-NAY-ter). A metering device which
  is used to add chlorine to water.
chlorine-contact chamber. That part of a water treatment
  plant where effluent is disinfected by chlorine.
chlorine demand. Chlorine demand is the difference
  between the amount of chlorine added to water and the
  amount of residual chlorine remaining after a given contact
  time. Chlorine demand may change with dosage, time,
  temperature, pH, and nature and amount of the impurities in
  the water.
  Chlorine Demand, mg/L = Chlorine Applied, mg/L - Residual, mg/L

chlorine requirement. The amount of chlorine which is
  needed for a particular purpose. Some reasons for adding
  chlorine are reducing the number of coliform bacteria (Most
  Probable Number), obtaining a particular chlorine residual,
  or oxidizing some substance in the water. In each case a
  definite dosage of chlorine will be necessary. This dosage is
  the chlorine requirement.
chlorophenolic (klor-o-FEE-NO-lick). Chlorophenolic
  compounds are phenolic compounds (carbolic acid)
  combined with chlorine.
chlorophenoxy (KLOR-o-fuh-KNOX-ee). A class of
  herbicides that may be found in domestic water supplies
  and cause adverse health effects. Two widely used
  chlorophenoxy herbicides are 2,4-D (2,4-Dichlorophenoxy
  acetic acid) and 2,4,5-TP (2,4,5-Trichlorophenoxy propi-
  onic acid (silvex)).
chlororganic (klor-or-GAN-nick). Organic compounds
  combined with chlorine. These compounds generally
  originate from, or are associated with, life processes such as
  those of algae in water.
chronic. Occurring over a long period of time, either continu-
  ously or intermittently; used to describe ongoing exposures
  and effects that develop only after a long exposure.
chronic exposure. Long-term, low-level exposure to atoxic
circle of influence. The circular outer edge of a depression
  produced in the water table by the pumping of water from a
  well. Also see cone of influence and cone of depression.
circuit. The complete path of an electric current, including
  the generating apparatus or other  source; or, a specific
  segment or section of the complete path.
circuit breaker. A safety device in an electrical circuit that
  automatically shuts off the circuit when it becomes over-
  loaded. The device can be manually reset.
cistern (SIS-turn). A small tank (usually covered) or a
  storage facility used to store water for a home or farm.
  Often used to store rain water.
clarifer (KLAlR-uh-fire). A large circular or rectangular
  tank or basin in which water is held for a period of time,
  during which the heavier suspended solids settle to the
  bottom. Clarifiers are also called  SETTLING BASINS and
class (pipe and fittings). The working pressure rating of a
  specific pipe for use in water distribution systems which i
  includes allowances for surges. This term is used for cast
  iron, ductile iron, asbestos cement and some plastic pipe.
clay. One type of soil particle with a diameter of approxi-
  mately one ten-thousandth of an inch.
clay soil. A soil containing more than 40 percent clay, but
  less than 45 percent sand, and less than 40 percent silt.
clear well. A reservoir for the storage of filtered water of

                                             Drinking Water Glossary
  sufficient capacity to prevent the need to vary the filtration
  rate with variations in demand. Also used to provide
  chlorine contact time for disinfection.
clinical studies. Studies of humans suffering from symptoms
  induced by chemical exposure.
coagulant aid. Any chemical or substance used to assist or
  modify coagulation.
coagulants (co-AGG-you-Ients). Chemicals that cause very
  fine particles to clump together into larger particles. This
  makes it easier to separate the solids from the water by
  settling, skimming, draining or filtering.
coagulation (co-AGG-you-LAY-shun). The clumping
  together of very fine particles into larger particles caused by
  the use of chemicals (coagulants). The chemicals neutralize
  the electrical charges of the fine particles and cause
  destabilization of the particles. This clumping together
  makes it easier to separate the solids from the water by
  settling, skimming, draining, or filtering.
cohesion, molecular attraction which holds two particles
coliform (COAL-i-form). A group of bacteria found in the
  intestines of warm-blooded animals (including humans) and
  also in plants, soil, air and water. Fecal coliforms are a
  specific class of bacteria which only inhibit the intestines of
  warm-blooded animals. The presence of coliform bacteria is
  an indication that the water is polluted and may contain
  pathogenic organisms.
coliform organism. Microorganisms found in the intestinal
  tract of humans and animals. Their presence in water
  indicates fecal pollution and potentially dangerous bacterial
  contamination by disease-causing microorganisms.
colloids (CALL-loids). Very small, finely divided solids
  (particles that do not dissolve) that remain dispersed in a
  liquid for a long time due to their small size and electrical
  charge. When most of the particles in water have a negative
  electrical charge, they tend to repel each other. This
  repulsion prevents the particles from clumping together,
  becoming heavier, and settling out.
colorimctric measurement. A means of measuring unknown
  chemical concentrations in water by measuring a sample's
  color intensity. The specific color of the sample, developed
  by addition of chemical reagents, is measured with a
  photoelectric colorimeter or is compared with "color
  standards" using, or corresponding with, known concentra-
  tions of the chemical.
combined available residual chlorine. The concentration of
  residual chlorine which is combined with ammonia (NH3)
  and/or organic nitrogen in water as a chloramine (or other
  chloro derivative) yet is still available to oxidize organic
  matter and utilize its bactericidal properties.
combined residual chlorination. The application of chlorine
  to water to produce combined available residual chlorine.
  This residual can be made up of monochloramines,
  dichloramines, and nitrogen trichloride.
combined sewer.  A sewer that transports surface runoff and
  human domestic wastes (sewage), and sometimes industrial
  wastes. Wastewater and runoff in a combined sewer may
  occur in excess of the sewer capacity and cannot be treated
  immediately. The excess is frequently discharged directly
  to a receiving stream without treatment, or to a holding
  basin for subsequent treatment and disposal.
community water system (C.W.S.). A public water system
  which serves at least 15 service connections used by year-
  round residents or regularly serves at least 25 year-round
  residents. Also see non-community water system, transient
  water system and non-transient non-community water
complete treatment. A method of treating water which
  consists of the addition of coagulant chemicals, flash
  mixing, coagulation - flocculation, sedimentation and
  filtration. Also called CONVENTIONAL FILTRATION.
compliance cycle. The nine-year calendar year cycle during
  which public water systems must monitor. Each compliance
  cycle consists  of three three-year compliance periods. The
  first calendar year cycle begins January 1, 1993 and ends
  December 31,2001; the second begins January 1,2002 and
  ends December 31,2010; the third from January 1,2011 to
  December 31, 2019, etc.
compliance period. A three year calendar period within a
  compliance cycle. Each compliance cycle has three three-
  year compliance periods. Within the first compliance cycle,
  the first compliance period runs  from January 1, 1993 to
  December 31,1995; the second from January 1, 1996 to
  December 31,1998; the third from January 1, 1999 to
  December 31,2001.
composite (proportional) samples (come-PAH-zit). A
  composite sample is a collection of individual samples
  obtained at regular intervals, usually every one or two hours
  during a 24-hour time span. Each individual sample is
  combined with the others in proportion to the rate of flow
  when the sample was collected The resulting mixture
  (composite sample) forms a representative sample and is
  analyzed to determine the average conditions during the
  sampling period.
composting.  A controlled microbial degradation of organic
  waste yield an environmentally sound, nuisance-free
  product of potential value as a soil conditioner.
compound. A substance composed of two or more elements
  whose composition is constant. For example, table salt
  (sodium chloride - NaCl) is a compound.
concentration polarization. 1) The ratio of the salt concen-
  tration in the membrane boundary layer to the salt concen-
  tration in the bulk stream. The most common and serious
  problem resulting from concentration polarization is the
  increasing tendency for precipitation of sparingly soluble
  salts and the deposition of particulate matter on the mem-
  brane surface. 2) Used in corrosion studies to indicate a
  depletion of ions near an electrode. 3) The basis for
  chemical analysis by a polarograph.

                                             Drinking Water Glossary
conductance. A rapid method of estimating the dissolved-
  solids content of a water supply. The measurement indicates
  the capacity of a sample of water to carry an electrical
  current, which is related to the concentration of ionized  v
  substances in the water. Also called SPECIFIC CONDUC-
conductivity. A measure of the ability of a solution (water) to
  carry an electric current.
conductor. A substance, body, device or wire that readily
  conducts or carries electrical current.
cone of depression. The depression, roughly conical in
  shape, produced hi the water table by the pumping of water
  from a well. Also see circle of influence and cone of
cone of influence. The depression, roughly conical in shape,
  produced in the  water table by the pumping of water from a
  well. Also see circle of influence and cone of depression
confined aquifer. An aquifer in which ground water is
  confined under pressure which is significantly greater than
  atmospheric pressure. See artesian aquifer.
confluent growth. A continuous bacterial growth covering
  the entire filtration area of a membrane filter, or a portion
  thereof, hi which bacterial colonies are not discrete.
confounding factors. Variables other than chemical exposure
  level which can  affect the incidence or degree of a param-
  eter being measured.
consumptive use. Water removed from available supplies
  without direct return to a water resource system for uses
  such as manufacturing, agriculture, and food preparation.
contactor. An electrical switch,  usually magnetically
contaminant. Any physical, chemical, biological, or radio-
  logical substance or matter that has an adverse effect on air,
  water, or soil.
contamination. The introduction into water of microorgan-
  isms, chemicals, toxic substances, wastes, or wastewater hi
  a concentration that makes the water unfit for its next
  intended use.
continuous sample. A flow of water from a particular place
  in a plant to the  location where samples are collected for
  testing. This continuous stream may be used to obtain grab
  or composite samples. Frequently, several taps (faucets)
  will flow continuously in the laboratory to provide test
  samples from various places in a water treatment plant.
contour farming. A conservation-based method of farming
  in which all farming operations (for example, tillage and
  planting) are performed across (rather than up and down)
  the slope. Ideally, each crop row is planted  at right angles
  to the ground slope.
contour strip farming. A kind  of contour farming in which
  row crops are planted in strips, between alternating strips of
  close-growing, erosion resistant forage (grass, grain or hay)
control loop. The path through the control system between
  the sensor, which measures a process variable, and the
  controller, which controls or adjusts the process variable.
control system. A system which senses and controls its own
  operation on a close, continuous basis in what is called
  proportional (or modulating) control.
controller. A device which controls the starting, stopping, or
  operation of a device or piece of equipment.
conventional filtration. A method of treating water to
  remove particulates. The method consists  of the addition of
  coagulant chemicals, flash mixing, coagulation - floccula-
  tion, sedimentation and filtration. Also called COMPLETE
  TREATMENT. Also see direct filtration and in-line
conventional filtration treatment. A series of processes
  including coagulation, flocculation, sedimentation, and
  filtration resulting hi substantial particulate removal.
conventional tillage.  The traditional method of farming hi
  which soil is prepared for planting by completely inverting
  it with a moldboard plow. Subsequent working of the soil
  with other implements is usually performed to smooth the
  soil surface.  Bare soil is exposed to the weather for some
  varying length of tune depending on soil and climatic
conventional treatment. See conventional  filtration Also
conveyance loss. Water lost in conveyance  (pipe, channel,
  conduit, ditch) by leakage or evaporation.
corporation stop. A water service shutoff valve located at a
  street water main. This valve cannot be operated from the
  ground surface because it is buried and there is no valve
  box. Also called a CORPORATION COCK.
corrosion. The gradual decomposition or destruction of a
  material by chemical action, often due to an electrochemi-
  cal reaction. Corrosion may be caused by: 1) stray current
  electrolysis, 2) galvanic corrosion caused by dissimilar
  metals, or 3) differential concentration cells. Corrosion
  starts at the surface of a material and moves inward.
corrosion inhibitor. A substances that slows the rate of
  corrosion of metal plumbing materials by  water, especially
  lead and copper materials, by forming a protective film on
  the interior surface of those materials.
corrosivity. An indication of the corrosiveness of a water.
  The corrosiveness of a water is described by the water's pH,
  alkalinity, hardness, temperature, total dissolved solids,
  dissolved oxygen concentration, and the Langelier Index.
cost/benefit analysis. A quantitative evaluation of the costs
  which would be incurred versus the overall benefits to
  society of a proposed action such as the establishment of an
  acceptable dose of a toxic chemical.
cost sharing. A publicly financed program through which
  society, as the beneficiary of environment protection, shares
  part of the cost of pollution control with those who must

                                             Drinking Water Glossary
  actually install the controls.
coulomb (COO-lahm). A measurement of the amount of
  electrical charge conveyed in one second by an electric
  current of one ampere. One coulomb equals about 6.25 x
  10U electrons (6,250,000,000,000,000,000 electrons).
coupon. A steel specimen inserted into water to measure the
  corrosiveness of water. The rate of corrosion is measured as
  the loss of weight of the coupon (in milligrams) per surface
  area (in square decimeters) exposed to the water per day. 10
  decimeters = 1 meter = 100 centimeters
cover crop. A crop that provides temporary protection for
  delicate seedlings and/or provides a canopy for seasonal soil
  protection and improvement between normal crop produc-
  tion periods. Except in orchards where permanent vegeta-
  tive cover is maintained, cover crops usually are grown for
  one year of less.  When plowed under and incorporated into
  the soil, cover crops are also referred to as gren manure
crop rotation. A system of farming in which a regular
  succession of different crops are planted on the same  land
  area, as opposed to growing the same crop time after time
cross-connection.  Any actual or potential connection
  between a drinking (potable) water system and an
  unapproved water supply or other source of contamination.
  For example, if you have a pump moving nonpotable water
  and hook into the drinking water system to supply water for
  the pump seal, a cross-connection or mixing between the
  two water systems can occur. This mixing may lead to
  contamination of the drinking water. Also see backsiphon-
CT or CTcalc. The product of "residual disinfectant concen-
  tration" (C) in mg/1 determined before or at the first
  customer, and the corresponding "disinfectant contact time"
  (T) in minutes, i.e., "C" x "T". If a public water system
  applies disinfectants at more than one point prior to the first
  customer, it must determine the CT of each disinfectant
  sequence before or at the first customer to determine the
  total percent inactivation or "total inactivation ratio."  In
  determining the total inactivation ratio, the public water
  system must determine the residual disinfectant concentra-
  tion of each disinfection sequence and corresponding
  contact time before any subsequent disinfection application
  point(s). "CTj,,," is the CT value required for 99.9 percent
  (3-log) inactivation of Giardia lamblia cysts. CT999 a variety
  of disinfectants and conditions appear hi Tables 1.1-1.6,2.1,
  and 3.1 of section 141.74(b)(3) in the code of Federal
CTW^ is the inactivation ratio. The sum of the inactivation
  ratios, or total inactivation ratio shown as

        2 = (CTcaIC)/(CT99,)

        is calculated by adding together the inactivation ratio
  for each disinfection sequence. A total inactivation ratio
  equal to or greater than 1.0 is assumed to provide a 3-log
  inactivation of Giardia lamblia cysts.
cumulative exposure. The summation of exposures of an
  organism to a chemical over a period of time.
curb stop. A water service shutoff valve located in a water
  service pipe near the curb and between the water main and
  the building. This valve is usually operated by a wrench or
  valve key and is used to start or stop flows in the water
  service line to a building. Also called a "curb cock."
curie. A measure of radioactivity. One Curie of radioactivity
  is equivalent to 3.7 x 10' or 37,000,000,000 nuclear
  disintegrations per second.
current. A movement or flow of electricity. Water flowing in
  a pipe is measured in gallons per second past a certain
  point, not by the number of water molecules going past a
  point. Electric current is measured by the number of
  coulombs per second flowing past a certain point in a
  conductor.  A coulomb is equal to about 6.25 x 1018 elec-
  trons (6,250,000,000,000,000,000 electrons). A flow of one
  coulomb per second is called one ampere, the unit of the
  rate of flow of current.


dateometer (day-TOM-uh-ter). A small calendar disc
  attached to motors and equipment to indicate the year in
  which the last maintenance service was performed.
day tank. A  tank used to store a chemical solution of known
  concentration for feed to a chemical feeder. A day tank
  usually stores sufficient chemical solution to properly treat
  the water being treated for at least one day. Also called an
dead end. The end of a water main which is not connected to
  other parts  of the distribution system by means of a con-
  necting loop of pipe
decant To draw off the upper layer of liquid (water) after the
  heavier material (a solid or another liquid) has settled.
dechlorination (dee-KLOR-uh-NAY-shun). The deliberate
  removal of chlorine from water. The partial or complete
  reduction of residual chlorine by any chemical or physical
decibel (DES-uh-bull). A unit for expressing the relative
  intensity of sounds on a scale from zero for the average
  least perceptible sound to about  130 for the average level at
  which sound causes pain to humans.
decomposition. The conversion of chemically unstable
  materials to more stable forms by chemical or biological
  action. If organic matter decays when there is no oxygen
  present (anaerobic conditions or putrefaction), undesirable
  tastes and odors are produced. Decay of organic matter
  when oxygen is present (aerobic conditions) tends to
  produce much less objectionable tastes and odors.
defluoridation (de-FLOOR-uh-DAY-shun). The removal

                                             Drinking Water Glossary
  of excess fluoride in drinking water to prevent the mottling
  (brown stains) of teeth.
degasification (DEE-GAS-if-uh-KAY-shun). A water
  treatment process which removes dissolved gases from the
  water. The gases may be removed by either mechanical or
  chemical treatment methods or a combination of both.
degradation. Chemical or biological breakdown of a
  complex compound into simpler compounds.
demineralization (DEE-MIN-er-al-uh-ZAY-shun). A
  treatment process which removes dissolved minerals (salts)
  from water.
denitrification. The biochemical conversion of nitrate and
  nitrite nitrogen in the soil dissolved in water to gaseous
density (DEN-sit-tee). A measure of how heavy a substance
  (solid, liquid or gas) is for its size. Density is expressed in
  terms of weight per unit volume, that is, grams per cubic
  centimeter or pounds per cubic foot. The density of water is
  1.0 gram per cubic centimeter or about 62.4 pounds per
  cubic foot.
dermal exposure. Contact between a chemical and the skin.
desalinization (DEE-SAY-Ieen-uh-ZAY-shun). The
  removal of dissolved salts (such as sodium chloride, NaCl)
  from water by natural means (leaching) or by specific water
  treatment processes.
desiccant (DESS-uh-kant). A drying agent which is capable
  of removing or absorbing moisture from the atmosphere in
  a small enclosure.
desiccation (DESS-uh-KAY-shun). A process used to
  thoroughly dry air; to remove virtually all moisture from
desiccator (DESS-uh-KAY-tor). A closed container into
  which heated weighing or drying dishes are placed to cool
  in a dry environment. The dishes may be empty or they may
  contain a sample. Desiccators contain a substance, such as
  anhydrous calcium chloride, which absorbs moisture and
  keeps the relative humidity near zero so that the dish or
  sample will not gain weight from absorbed moisture.
destratification (de-STRAT-uh-fuh-KAY-shun). The
  development of vertical mixing within a lake or reservoir to
  eliminate (either totally or partially) separate layers of
  temperature, plant, or animal life. This vertical mixing can
  be caused by mechanical means (pumps) or through the use
  of forced ah- diffusers which release air into the lower
  layers of the reservoir.
detention lag. The time period between the moment a change
  is made and the moment when such a change is finally
  sensed by the associated measuring instrument.
detention time. 1) The theoretical (calculated) time required
  for a small amount of water to pass through a tank at a
  given rate of flow. 2) The actual time in hours, minutes or
  seconds that a small amount of water is in a settling basin,
  flocculating basin or rapid-mix chamber. In storage
  reservoirs, detention time is the length of time entering
  water will be held before being drafted for use (several
  weeks to years, several months being typical).
Detention Time (hr) =
        Basin Volume (gal.)(24 hr/day)/ Flow (gal/day)

dew point. The temperature to which air with a given
  quantity of water vapor must be cooled to cause condensa-
  tion of the vapor in the air.
dewater. 1) To remove or separate a portion of the water
  present in a sludge or slurry. To dry sludge so it can be
  handled and disposed. 2) To remove or drain the water from
  a tank or a trench.
diatomaceous earth. A fine, siliceous (made of silica)
  "earth" composed mainly of the skeletal remains of dia-
  toms, a type of free-floating, microscopic plant found in the
diatomaceous earth filtration (DE filtration). A filtration
  method resulting in  substantial particulate removal, that
  uses a process in which: 1) a "precoat" cake of diatoma-
  ceous earth filter media is deposited on a support membrane
  (septum), and 2) while the water is filtered by passing
  through the cake on the septum, additional filter media,
  known as "body feed," is continuously added to the feed
  water to maintain the permeability of the filter cake.
diffusion. The movement of suspended or dissolved particles
  from a more concentrated to a less concentrated region as a
  result of the random movement of individual particles; the
  process tends to distribute them uniformly througout the
  available volume.
digital readout. Use of numbers to indicate the value or
  measurement of a variable. The readout of an instrument by
  a direct, numerical reading of the measured value.
dilute solution. A solution that has been made weaker
  usually by the addition of water.
dimictic (die-MlCK-tick). Lakes and reservoirs which freeze
  over and normally go through two stratification and two
  mixing cycles within a year.
direct current (D.C.). Electrical current flowing hi one
  direction only and essentially free from pulsation.
direct filtration. A filtration method of treating water which
  consists of the addition of coagulant chemicals, flash
  mixing, coagulation, minimal flocculation, and filtration.
  The flocculation facilities may be omitted, but the physical-
  chemical reactions will occur to some extent. The sedimen-
  tation process is omitted. Also see conventional filtration
  and in-line filtration.
direct runoff.  Water that flows over the ground surface or
  through the ground  directly into streams, rivers, or lakes.
discharge head. The  pressure (hi pounds per square inch or
  psi) measured at the centerline of a pump discharge and
  very close to the discharge flange, converted into feet.
disinfectant. Any oxidant, including but not limited to

                                             Drinking Water Glossary
  chlorine, chlorine dioxide, chloramines, and ozone, that is
  added to water in any part of the treatment or distribution
  process and is intended to kill or inactivate pathogenic
disinfectant contact time ("T" in CT calculations). The
  time in minutes that it takes for water to move from the
  point of disinfectant application or the previous point of
  disinfectant residual measurement to a point before or at the
  point where residual disinfectant concentration (C) Is
  measured. Where only one C is measured. T is the time in
  minutes that it takes for water to move from the point of
  disinfectant application  to a point before or at where
  residual disinfectant concentration (C) is measured. Where
  more than one C is measured, T is (a) for the first measure-
  ment of C, the time in minutes that it takes for water to
  move from the first or only point of disinfectant application
  to a point before or at the point where the firstC+ is
  measured and (b) for subsequent measurements of C, the
  time in minutes mat it takes for water to move from the
  previous C measurement point to the C measurement point
  for which the particular T is being calculated. Disinfectant
  contact time in pipelines must be calculated based on plug
  flow by dividing the internal volume of the pipe by the
  maximum hourly flow rate through that pipe. Disinfectant
  contact time within mixing basins and storage reservoirs
  must be determined by tracer studies or an equivalent
disinfection. The process designed to kill most microorgan-
  isms in water, including essentially all pathogenic (disease-
  causing) bacteria. There are several ways to disinfect, with
  chlorine being most frequently used in water treatment.
  Compare with sterilization.
disinfection by-product A compound formed by the
  reaction of a disinfectant such as chlorine with organic
  material in the water supply.
dissolved oxygen (DO). Measure of water quality indicating
  free oxygen dissolved in water.
distillate (DIS-tuh-late). In the distillation of a sample, a
  portion is evaporated; the part that is condensed afterwards
  is the distillate.
divalent (die-VAY-lent). Having a valence of two, such as
  the ferrous ion, Fe2*.
diversion.  1)  Use of part of a stream flow as a water
  supply. 2) A structural conveyance (or ditch) constructed
  across a slope to intercept runoff flowing down a hillside,
  and divert it to some convenient discharge point.
Domestic or Other Non-distribution System Plumbing
  Problem. A coliform contamination problem in a public
  water system with more than one service connection that is
  limited to the specific service connection from which the
  coliform positive sample was taken.
 dosage. The quantity of a chemical administered to an
 dose. The actual quantity of a chemical to which an organism
  is exposed. See absorbed dose.
dose equivalent. The product of the absorbed dose from
  ionizing radiation and such factors as account for differ-
  ences In biological effectiveness due to the type of radiation
  and is distribution hi the body as specified by the Interna-
  tional Commission on Radiological Units and Measure-
  ments (ICRU).
dose-response. A quantitative relationship between the dose
  of a chemical and an effect caused by the chemical.
dose-response curve. A graphical presentation of the
  relationship between degree of exposure to a chemical
  (dose) and observed biological effect or response.
dose-response evaluation. A component of risk assessment
  that describes the quantitative relationship between the
  amount of exposure to a substance and the extent of toxic
  injury or disease.
dose-response relationship. The quantitative relationship
  between the amount of exposure to a substance and the
  extent of toxic injury produced.
downgradients. The direction that ground water flows;
  similar in concept to:  downstream for surface water, such
  as a river.
DPD (pronounce as separate letters). A method of measur-
  ing the chlorine residual hi water. The residual may be
  determined by either titrating or comparing a developed
  color with color standards. DPD stands for N,N-diethyl-p-
draft.  1) The act of drawing or removing water from a tank
  or reservoir. 2) The water which is drawn or removed from
  a tank or reservoir.
drainage. A technique to improve the productivity of some
  agricultural land by removing excess water from the soil;
  surface drainage is accomplished with open ditches;
  subsurface drainage uses porous conduits (drain tile) buried
  beneath the soil surface.
drainage basin. The area of land that drams water, sediment,
  and dissolved materials to a common outlet at some point
  along a stream channel. Also see watershed.
drawdown. 1) The drop in the water table or level of water hi
  the ground when water is being pumped from a well. 2) The
  amount of water used from a tank or reservoir. 3) The drop
  in the water level of a tank or reservoir.
DWEL (Drinking Water Equivalent Level). Estimated
  exposure (hi mg/L) which is interpreted to be protective for
  non-carcinogenic endpoints of toxicity over a lifetime of
  exposure. DWEL was developed for chemicals that have a
  significant carcinogenic potential (Group B). Provides risk
  manager with evaluation on non-cancer endpoints, but
  infers that carcinogenicity should be considered the toxic
  effect of greatest concern.
 dynamic pressure. When a pump is operating, the vertical
  distance (in feet) from a reference point (such as a pump
  centerline) to the hydraulic grade line is the dynamic head.

                                              Drinking Water Glossary
eductor (e-DUCK-ter). A hydraulic device used to create a
  negative pressure (suction) by forcing a liquid through a
  restriction, such as a Venturi. An eductor or aspirator (the
  hydraulic device) may be used in the laboratory in place of
  a vacuum pump. As an injector, it is used to produce
  vacuum for chlorinators.
effective corrosion inhibitor residual. A concentration of
  corrosion inhibitor sufficient to form a protective coating on
  the interior walls of a pipe, reducing its corrosion.
effective range. That portion of the design range (usually
  upper 90 percent) in which an instrument has acceptable
  accuracy. Also see range and span
effective size (E.S.). The diameter of the particles in a
  granular sample (filter media) for which 10 percent of the
  total grains are smaller and 90 percent larger on a weight
  basis. Effective size is obtained by passing granular
  material through sieves with varying dimensions of mesh
  and weighing the material retained by each sieve. The
  effective size is also approximately the average size of the
effluent (EF-loo-ent). Water or some other liquid-raw,
  partially or completely treated-flowing from a reservoir,
  basin, treatment process or treatment plant.
ejector. A device used to disperse a chemical solution into
  water being treated.
electrochemical reaction. Chemical changes produced by
  electricity (electrolysis) or the production of electricity by
  chemical changes (galvanic action). In corrosion, a chemi-
  cal reaction is accompanied by the flow of electrons
  through a metallic path. The electron flow may come from
  an external force and cause the reaction, such as electrolysis
  caused by a B.C. (direct current) electric railway or the
  electron flow may be caused by a chemical reaction as in
  the galvanic action of a flashlight dry cell.
electrochemical sries. A list of metals with the standard
  electrode potentials given in volts. The size and sign of the
  electrode potential indicates how easily these elements will
  take on or give up electrons, or corrode. Hydrogen is
  conventionally assigned a value of zero.
electrolysis (ee-leck-TRAWL-uh-sis). The decomposition of
  material by an outside electrical current.
electrolyte (ee-LECK-tro-LlGHT). A substance which
  dissociates (separates) into two or more ions when it is
  dissolved hi water.
electrolytic cell (ee-LECK-tro-LlT-ick). A device in which
  the chemical decomposition of material causes an electric
  current to flow. Also, a device hi which a chemical reaction
  occurs as a result of the flow of electric current. Chlorine
  and caustic (NaOH) are made from salt (Nad) in electro-
  lytic cells.
electromotive force (E.M.F.). The electrical pressure
  available to cause a flow of current (amperage) when an
  electrical circuit is closed. See voltage
 electromotive series. A list of metals and alloys presented in
  the order of their tendency to corrode (or go into solution).
  Also called the Galvanic Series. This is a practical applica-
  tion of the theoretical ELECTROCHEMICAL SERIES.
 electron. An extremely small, negatively charged particle;
  the part of an atom that determines its chemical properties.
 element. A substance which cannot be separated into its
  constituent parts and still retain its chemical identity. For
  example, sodium (Na) is an element.
 end bells. Devices used to hold the rotor and stator of a motor
  in position.
 end point. Samples are titrated to the end point. This means
  that a chemical is added, drop by drop, to a sample until a
  certain color change (blue to clear, for example) occurs.
  This is called the END POINT of the titration. In addition
  to a color change, an end point may be reached by the
  formation of a precipitate or the reaching of a specified pH.
  An end point may be detected by the use of an electronic
  device such as a pH meter.
 endangerment assessment. A site-specific risk assessment
  of the actual or potential danger to human health or welfare
  and the environment from the release of hazardous sub-
  stances or waste. The endangerment assessment document
  is prepared hi support of enforcement actions under
 endemic (en-DEM-ick). Something peculiar to a particular
  people or locality, such as a disease which is always present
  hi the population.
endrin (EN-drin). A pesticide toxic to freshwater and marine
  aquatic life that produces adverse health effects hi domestic
  water supplies.
energy grade line (E.G.L.). A line that represents the
  elevation of energy head of water flowing hi a pipe, conduit
  or channel. The  line is drawn  above the hydraulic grade line
  (gradient) a distance equal to the velocity head (V2/2g) of
  the water flowing at each section or point along the pipe or
  channel. Also see hydraulic gradeline.
enteric. Of intestinal origin, especially applied to wastes or
entrain. To trap bubbles hi water either mechanically through
  turbulence or chemically through a reaction.
enzymes (EN-zimes). Organic substances (produced by
  living organisms) which cause or speed up chemical
  reactions. Organic catalysts and/or biochemical catalysts.
E.P.A. United States Environmental Protection Agency.
epidemic. Widespread outbreak of a disease, or a large
  number of cases of a disease hi a single community or
  relatively small area. Disease may spread from person to
  person, and/or by the exposure of many persons to a single
  source, such as a water supply.
epidemiologic study. Study of human populations to identify
  causes of disease. Such studies often compare  the health

                                             Drinking Water Glossary
  status of a group of persons who have been exposed to a
  suspect agent with that of a comparable non-exposed group.
epidemiology (EP-uh-DE-me-ALL-o-gee). A branch of
  medicine which studies epidemics (diseases which affect
  significant numbers of people during the same time period
  in the same  locality). The objective of epidemiology is to
  determine the factors that cause epidemic diseases and how
  to prevent them.
epilimnion (EP-uh-LlM-knee-on). The upper layer of water
  in a thermally stratified lake or reservoir. This layer consists
  of the warmest water and has a fairly uniform (constant)
  temperature. The layer is readily mixed by wind action.
erosion.  Wearing away of soil by running water, wind, or
  ice; erosion is the process by which the earth's surface is
  shaped and  occurs even hi remote, uninhabited areas at a
  slow rate (geologic erosion); of more concern is accelerated
  erosion caused by people's activities.
ester. A compound formed by the reaction between an acid
  and an alcohol with the elimination of a molecule of water.
eutrophic (you-TRO-fick). Reservoirs and lakes which are
  rich in nutrients and very productive in terms of aquatic
  animal and  plant life.
eutrophication (you-TRO-fi-KAY-shun). The increase in
  the nutrient levels of a lake or other body of water; this
  usually causes  an increase in the growth of aquatic animal
  and plant life.
evaporation. The process by which water or other liquid
  becomes a gas (water vapor or ammonia vapor). Water
  from land areas, bodies of water, and all other moist
  surfaces is absorbed into the atmosphere as a vapor.
cvapotranspiration (ee-VAP-o-TRANS-purr-A-shun). The
  combined processes of evaporation and transpiration. It can
  be defined as the sum of water used by vegetation and water
  lost by evaporation.
exemption. A State with primacy may relieve a public water
  system from a requirement respecting an MCL, treatment
  technique or both, by granting an exemption if certain
  conditions exist. These are: 1) the system cannot comply
  with a MCL or treatment technique due to compelling
  factors which may include economic factors; 2) the system
  was in operation on the effective date of the MCL or
  treatment technique requirement; and 3) the exemption will
  not result in an unreasonable  public health risk. Also see
 exposure.  Contact with a chemical or physical agent.
 exposure assessment The determination or estimation
  (qualitative or quantitative) of the magnitude, frequency,
  duration, route, and extent (number of people) of exposure
  to a chemical.
 exposure coefficient Term which combines information on
  the frequency, mode, and magnitude of contact with
  contaminated medium to yield a quantitative value of the
  amount of contaminated medium contacted per day.
exposure level (chemical). The amount (concentration) of a
  chemical at the absorptive surfaces of an organism.
exposure scenario. A set of conditions or assumptions about
  sources, exposure pathways, concentrations of toxic
  chemicals and populations (numbers, characteristics and
  habits) which aid the investigator in evaluating and quanti-
  fying exposure in a given situation.
extrapolation. Estimation of unknown values by extending or
  projecting from known values.
facultative (FACK-ul-TAY-tive). Facultative bacteria can
  use either molecular (dissolved) oxygen or oxygen obtained
  from food material such as sulfate or nitrate ions. In other
  words, facultative bacteria can live under aerobic or
  anaerobic conditions.
fecal coliform bacteria. Bacteria found in the intestinal tracts
  of mammals. Their presence in water or sludge is an
  indicator of pollution and possible contamination by
feedback. The circulating action between a sensor measuring
  a process variable and the controller which controls or
  adjusts the process variable .
filtration. A process for removing particulate matter from
  water by passage through porous media.
finished water. Water that has passed through a water
  treatment plant; all the treatment processes are completed or
  "finished". This water is ready to be delivered to consum-
  ers. Also called PRODUCT WATER.
first draw. The water that immediately comes out when a tap
  is first opened. This water is likely to have the highest level
  of lead contamination from plumbing materials.
first draw sample. A one-liter sample of tap water, collected
  in accordance with CFR Section 141.86(b)(2), that has been
  standing in plumbing pipes at least 6 hours and is collected
  without flushing the tap.
fix, sample. A sample is fixed in the field by adding chemi-
  cals that prevent the water quality indicators of interest in
  the sample from changing before final measurements are
  performed later in the lab.
flagellates (FLAJ-el-LATES). Microorganisms that move
  by the action of tail-like projections.
flame polished. Melted by a flame to smooth out irregulari-
  ties. Sharp or broken edges of glass (such as the end of a
  glass tube) are rotated in a flame until the dge melts slightly
  and becomes smooth.
 floe. Clumps of bacteria and particulate impurities that have
  come together and formed a cluster. Found in flocculation
  tanks and settling or sedimentation basins.
 flocculation. The gathering togetiier of fine particles hi water
  by gentle mixing after the addition of coagulant chemicals
  to form larger particles.

                                             Drinking Water Glossary
floodplain. The flat or nearly flat land on the floor of a
  steam valley or tidal area that is covered by water during
fluidized (FLEW-id-i-zd). A mass of solid particles that is
  made to flow like a liquid by injection of water or gas is
  said to have been fluidized. In water treatment, a bed of
  filter media is fluidized by backwashing water through the
fluoridation (FLOOR-uh-DAY-shun). The addition of a
  chemical to increase the concentration of fluoride ions in
  drinking water to a predetermined optimum limit to reduce
  the incidence (number) of dental caries (tooth decay) in
  children. Defluoridation is the removal of excess fluoride in
  drinking water to prevent the mottling (brown stains) of
fluorosis. An abnormal condition caused by excessive intake
  of fluorine, characterized chiefly by mottling of the teeth.
flush. l)To open a cold-water tap to clear out all the water
  which may have been sitting for a long time in the pipes, in
  new homes, to flush a system means to send large volumes
  of water gushing through the unused pipes to remove loose
  particles of solder and flux. 2) To force large amounts of
  water through liquid to clean out piping or tubing, storage
  or process tanks.
flushing. A method used to clean water distribution lines.
  Hydrants are opened and water with a high velocity flows
  through the pipes, removes deposits from the pipes, and
  flows out the hydrants.
flux. A flowing or flow.
foot valve. A special type of check valve located at the .
  bottom end of the suction pipe on a pump. This valve opens
  when the pump operates to allow water to enter the suction
  pipe but closes when the pump shuts off to prevent water
  from flowing out of the suction pipe.
formation. A group of similar consolidation (that is, rela-
  tively solid) rocks of unconsolidated (that is, relatively
  loose) minerals.
free available residual chlorine. That portion of the total
  available residual chlorine composed of dissolved chlorine
  gas (C12), hypochlorous acid (HOC1), and/or hypochlorite
  ion (OC1") remaining in water after chlorination. This does
  not include chlorine that has combined with ammonia,
  nitrogen, or other compounds.
free residual chlorination. The application of chlorine to
  water to produce a free available chlorine residual equal to
  at least 80 percent of the total residual chlorine (sum of free
  and combined available chlorine residual).
freeboard. 1) The vertical distance from the normal water
  surface to the top of the confining wall. 2) The vertical
  distance from the sand surface to the underside of a trough
  in a sand filter. This distance is also  called AVAILABLE
friction losses. The head, pressure or energy (they are the
  same) lost by water flowing in a pipe or channel as a result
  of turbulence caused by the velocity of the flowing water
  and the roughness of the pipe, channel walls, and restric-
  tions caused by fittings. Water flowing in a pipe loses
  pressure or energy as a result of friction losses. Also see
  head loss.
fresh water. Water that generally contains less than 1,000
  milligrams-per-liter of dissolved solids
fungi (FUN-ji). Mushrooms, molds, mildews, rusts, and
  smuts that are small non-chlorophyll-bearing plants lacking
  roots, stems and leaves. They occur in natural waters and
  grow best in the absence of light. Their decomposition may
  cause objectionable tastes and odors in water.

gage pressure. The pressure within a closed container or pipe
  as measured with a gage. In contrast, absolute pressure is
  the sum of atmospheric pressure (14.7 Ibs/sq in) PLUS
  pressure within a vessel (as measured by a gage). Most
  pressure gages read in gage pressure or psig (pounds per
  square inch gage pressure).
galvnic call. An electrolytic cell capable of producing
  electrical energy by electrochemical action. The decomposi-
  tion of materials in the cell causes an electric (electron)
  current to flow from cathode to anode.
galvanic series. A list of metals and alloys presented in the
  order of their tendency to corrode (or go into solution). Also
  called the ELECTROMOTIVE SERIES. This is a practical
  application of the theoretical ELECTROCHEMICAL
galvanize. To coat a metal (especially iron or steel) with zinc.
  Galvanization is the process of coating a metal with zinc.
garnet (GAR-nit). A group of hard, reddish, glassy, mineral
  sands made up of silicates of base metals (calcium, magne-
  sium, iron  and manganese). Garnet has a higher density
  than sand.
gastroenteritis. An inflammation of the stomach and
  intestine resulting in diarrhea, with vomiting and cramps
  when irritation is excessive. When caused by an infectious
  agent, it is  often associated with fever.
gauge, pipe. A number that defines the thickness of the sheet
  used to make steel pipe. The larger the number, the thinner
  the pipe wall.
gavage. Type of exposure in which a substance is adminis-
  tered to an animal through a stomach tube.
geological log. A detailed description of all underground
  features discovered during the drilling of a well (depth,
  thickness and type of formations).
geophysical log. A record of the structure and composition of
  the earth encountered when drilling a well or similar type of
  test hole or boring.
germicide (GERM-uh-SlDE). A substance formulated to kill
  germs or microorganisms. The germicidal properties of
  chlorine make it an effective disinfectant.

                                              Drinking Water Glossary
Giardia Lamblia. Flagellate protozoan which is shed during
  its cyst stage into the feces of man and animals. When
  water containing these cysts is ingested, the protozoan
  causes a severe gastrointestinal disease called giardiasis.
giardiasis (gee-are-DYE-uh-sis). Intestinal disease caused
  by an infestation of Giardia flagellates.
glass, pipe and fittings. The working pressure rating of a
  specific pipe for use in water distribution systems which
  includes allowances for surges. This term is used for cast
  iron, ductile iron, asbestos cement and some plastic pipe.
gooseneck. A portion of a service connection between the
  distribution system water main and a meter. Sometimes
  called a pigtail.
grab sample. A single sample collected at a particular tune
  and place which represents the composition of the water
  only at that time and place.
grade. 1) The elevation of the invert of the bottom of a
  pipeline, canal,  culvert or similar conduit. 2) The inclination
  or slope of a pipeline,  conduit, stream channel, or natural
  ground surface; usually expressed in terms of the ratio  or
  percentage of number of units of vertical rise or fall per unit
  of horizontal distance. A 0.5 percent grade would be a  drop
  of one-half foot per hundred feet of pipe.
gram. A unit of mass equivalent to one milliliter of water at 4
  degrees Celsius. 1/454 of a pound.
gravimetric. A means of measuring unknown concentrations
  of water quality indicators in a sample by WEIGHING a
  precipitate or residue of the sample.
grey water. Wastewater other than sewage, such as sink
  drainage or washing machine  discharge.
ground water. The supply of fresh water found beneath the
  Earth's surface, usually in aquifers, which is often used for
  supplying wells and springs. Because ground water is a
  major source of drinking water there is growing concern
  over areas where leaching agricultural or industrial pollut-
  ants or substances from leaking underground storage tanks
  arc contaminating ground water.
ground water under the direct influence (UDI) of surface
  water. Any water beneath the surface of the ground with: 1)
  significant occurrence of Insects or other macroorganisms
  algae, or large-diameter pathogens such as Giardia lamblia
  or, 2) significant and relatively rapid shifts in water
  characteristics such as turbidity, temperature, conductivity,
  or pH which closely correlate to climatological or surface
  water conditions. Direct influence must be determined for
  individual sources in accordance with criteria established by
  the State. The State determination of direct influence may
  be based on site-specific measurements of water quality
  and/or documentation of well constructioncharacteristics
  and geology with field evaluation.
 gross alpha particle activity. The total radioactivity due to
  alpha particle emission as inferred from measurements on a
  dry sample.
 gross beta particle activity. The total radioactivity due to
 beta particle emission as inferred from measurements on a
 dry sample.

half-life. The length of time required for the mass, concentra-
 tion, or activity of a chemical or physical agent to be
 reduced by one-half.
halogen. One of the chemical elements chlorine, bromine, or
hard water. Alkaline water containing dissolved salts that
 interfere with some industrial processes and prevent soap
 from lathering. Water may be considered hard if it has a
 hardness greater than the typical hardness of water from the
 region. Some textbooks define hard water as water with a
 hardness of more than 100 mg/L as calcium carbonate.
hardness, water. A characteristic of water caused mainly by
 the salts of calcium and magnesium, such as bicarbonate,
 carbonate, sulfate, chloride and nitrate. Excessive hardness
 in water is undesirable because it causes the formation of
 soap curds, increased use of soap, deposition of scale in
 boilers, damage in some industrial processes, and some-
 times causes objectionable tastes in drinking water.
hazard evaluation. A component of risk assessment that
  involves gathering and evaluating data on the types  of
 health injury or disease (e.g., cancer) that may be produced
 by a chemical and on the conditions of exposure under
  which injury or disease is produced.
head. The vertical distance (in feet) equal to the pressure (in
  psi) at a specific point. The pressure head is equal to the
  pressure in psi times 2.31 ft/psi.
head loss. The head, pressure or energy (they are the  same)
  lost by water flowing in a pipe or channel as a result of
  turbulence caused by the velocity of the flowing water and
  the roughness of the pipe, channel walls or restrictions
  caused by fittings. Water flowing in a pipe loses head,
  pressure or energy as a result of friction losses. Also see
  friction losses.
header. A large pipe to which a series of smaller pipes are
  connected. Also called a MANIFOLD.
heat sensor. A device that opens and closes  a switch in
  response to changes in the temperature. This device might
  be a metal contact, or a thermocouple which generates a
  minute electrical current proportional to the difference in
  heat, or a variable resistor whose value changes in response
  to changes in temperature. Also called a TEMPERATURE
 heavy metals. Metallic elements with high atomic weights,
  e.g., mercury, chromium, cadmium, arsenic, and lead. They
  can damage living things at low concentrations and tend to
  accumulate in the food chain.
 hectare (HECK-tar). A measure of area in the metric system
  similar to an acre. One hectare is equal to  10,000 square
  meters and 2.4711 acres.

                                            Drinking Water Glossary
hematopoiesis. The production of blood and blood cells;
hepatic. Pertaining to the liver.
hepatitis (HEP-up-TlE-tis). Hepatitis is an inflammation of
  the liver usually caused by an acute viral infection. Yellow
 jaundice is one symptom of hepatitis.
hepatoma. A malignant tumor occurring in the liver.
herbicide (HERB-uh-SLDE). A compound, usually a man-
  made organic chemical, used to kill or control plant growth.
hertz. The number of complete electromagnetic cycles or
  waves in one second of an electrical or electronic circuit.
  Also called the frequency of the current. Abbreviated Hz.
heterotrophic microorganisms. Bacteria and other microor-
  ganisms that use organic matter synthesized by other
  organisms for energy and growth.
heterotrophic plate count (HPC). The number of colonies
  of heterotrophic bacteria grown on selected solid media at  a
  given temperature and incubation period, usually expressed
  hi number of bacteria per milliliter of sample.
high-line jumpers. Pipes or hoses connected to fire hydrants
  and laid on top of the ground to provide emergency water
  service for an isolated portion of a distribution system.
high-to-low-dose extrapolation. The process of prediction of
  low exposure risks to rodents from the measured high
  exposure-high risk data.
histology. The study of the structure of cells and tissues;
  usually involves microscopic examination of tissue slices.
hose bib. Faucet. A locatin in a water line where a hose is
HTH (pronounce as separate letters). High Test Hypochlo-
  rite. Calcium hypochlorite or Ca(OCl)2
human equivalent dose. A dose which, when administered
  to humans, produces an effect equal to that produced by a
  dose in animals.
human exposure evaluation. A component of risk assess-
  ment that involves describing the nature and size of the
  population exposed to a substance and the magnitude and
  duration of their exposure. The evaluation could concern
  past exposures, current exposures, or anticipated exposures.
human health risk. The likelihood (or probability) that a
  given exposure or series of exposures may have or will
  damage the health of individuals experiencing the expo-
humus. Organic portion of the soil remaining after prolonged
  microbial decomposition.
hydrated lime. Limestone that has been burned and treated
  with water'under controlled conditions until the calcium
  oxide portion has been converted to calcium hydroxide
  (Ca(OH)2). Hydrated lime is quicklime combined with
  water. CaO + Hp --> Ca(OH)2. Also see quicklime.
hydraulic grade line. The surface or profile of water flowing
  in an open channel or a pipe flowing partially full. If a pipe
  is under pressure, the hydraulic grade line is at the level
  water would rise to in a small vertical tube connected to the
  pipe. Also see energy grade line
hydraulic gradient. The slope of the hydraulic grade line.
  This is the slope of the water surface hi an open channel,
  the slope of the water surface of the groundwater table, or
  the slope of the water pressure for pipes under pressure.
hydrogeologic conditions. Conditions stemming from the
  interaction of ground water and the surrounding soil and
hydrogeologic cycle.  The natural process recycling water
  from the atmosphere down to (and through) the earth and
  back to the atmosphere again.
hydrogeology. The geology of ground water, with particular
  emphasis on the chemistry and movement of water.
hydrogeologist (HI-dro-gee-ALL-uh-gist). A person who
  studies and works with groundwater.
hydrograph. A graph of the rate of runoff plotted against
  tune for a point on a channel.
hydrologic cycle (HI-dro-LOJ-ick). Movement or exchange
  of water between the atmosphere and the earth.
hydrology. The study of the occurrence, distribution and
  circulation of the natural waters of the earth.
hydrolysis (hi-DROLL-uh-sis). A chemical reaction  in
  which a compound is converted into another compound by
  taking up water.
hydrophilic (Hi-dro-FlLL-ick). Having a strong affinity
  (liking) for water. The opposite of hydrophobic.
hydrophobic (Hi-dro-FOE-bick). Having a strong aversion
  (dislike) for water. The opposite of hydrophilic.
hydropneumatic (Hi-dro-new-MAT-ick). A water system,
  usually small, hi which a water pump is automatically
  controlled (started and stopped) by the ah- pressure hi a
  compressed-air tank.
hydrostatic pressure (Hi-dro-STAT-ick). 1) The pressure at
  a specific elevation exerted by a body of water at rest or, 2)
  In the case of groundwater, the pressure at a specific
  elevation due to the weight of water at higher levels hi the
  same zone of saturation.
hydrochlorination (Hi-poe-KLOR-uh-NAY-shun).  The
  application of hypochlorite compounds to water for the
  purpose of disinfection.
hydrochlorinators (Hi-poe-KLOR-uh-NAY-tors). Chlorine
  pumps, chemical feed pumps or devices used to dispense
  chlorine solutions made from hypochlorites such as  bleach
  (sodium hypochlorite) or calcium hypochlorite into  the
  water being treated.
hypochlorite (Hi-poe-KLOR-ite). Chemical compounds
  containing available chlorine; used for disinfection.  They
  are available as liquids (bleach) or solids (powder, granules
  and pellets). Salts of hypochlorous acid.
hypolimnion (Hi-poe-LlM-knee-on). The lowest layer hi a

                                              Drinking Water Glossary
  thermally stratified lake or reservoir. This layer consists of
  colder, more dense water, has a constant temperature and no
  mixing occurs.
imhoff cone. A clear, cone-shaped container marked with
  graduations. The cone is used to measure the volume of
  settleable solids in a specific volume (usually one liter) of
impeller. A rotating set of vanes in a pump designed to pump
  or lift water.
impermeable (im-PURR-me-uh-BULL). Not easily
  penetrated. The property of a material or soil that des not
  allow, or allows only with great difficulty, the movement or
  passage of water.
incidence of tumors. Percentage of animals with tumors.
indicator (chemical). A substance that gives a visible
  change, usually of color, at a desired point in a chemical
  reaction, generally at a specified end point.
indicator (instrument). A device which indicates the result
  of a measurement. Most indicators in the water utility field
  use either a fixed scale and movable indicator (pointer) such
  as a pressure gage or a movable scale and movable indica-
  tor like those used on a circular-flow recording chart. Also
  called a RECEIVER.
infiltration. 1) The gradual flow or movement of water into
  and through (to percolate or pass through) the pores of the
  soil Also see percolation. 2) the penetration of water from
  the soil into sewer or  other pipes through defective joints,
  connections or manhole walls.
infiltration gallery. A subsurface groundwater collection
  system, typically shallow in depth, constructed with open-
  jointed or perforated pipes that discharge collected water
  into a water-tight chamber. From this chamber the water is
  pumped to treatment facilities  and into the distribution
  system. Infiltration galleries are usually located close to
  streams or ponds and may be under the direct influence of
  surface water.
infiltration rate. Quantity of water (usually measured in
  inches) that will enter a particular type of soil per unit tune
  (usually one hour).
influent (IN-flu-ent). Water or other liquid-raw or partially
  treated-flowing INTO a reservoir, basin, treatment process
  or treatment plant.
ingcstion. Type of exposure through the mouth.
inhalation. Type of exposure through the lungs.
initial  compliance period. The  first full three-year compli-
  ance period which begins at least 18 months  after promul-
in-line filtration. The addition of chemical coagulants
  directly to the filter inlet pipe.  The chemicals are mixed by
  the flowing water. Flocculation and sedimentation facilities
  are eliminated. This pretreatment method is commonly used
  in pressure filter installations. Also see conventional
  filtration and direct filtration.
inorganic. Material such as sand, salt, iron, calcium salts and
  other mineral materials. Inorganic substances are of mineral
  origin, whereas organic substances are usually of animal or
  plant origin. Also see organic.
input horsepower. The total power used in operating a pump
  and motor.
Input HP = (Brake HP)(100%)/Motor Efficiency, %
insecticide. Any substance or chemical formulated to kill or
  control insects.
in situ. In place, the original location, in the natural environ-
instream uses. Water uses that can be carried out without
  removing the water from its source, as in navigation and
integrated exposure assessment. A summation over tune, in
  all media, of the magnitude of exposure to a toxic chemical.
integrator. A device or meter that continuously measures and
  calculates (adds) total flows in gallons, or million cubic
  feet, or some other unit of volume measurement. Also
  called a TOTALIZER.
interface. The common boundary layer between two sub-
  stances such as water and a solid (metal); or between two
  fluids such as water and a gas (ah-); or between a liquid
  (water) and another liquid (oil).
interflow. Lateral movement  of water in the upper layer of
interlock. An electrical switch, usually magnetically oper-
  ated. Used to interrupt all (local) power to a panel or device
  when the door is opened or the circuit exposed to service.
internal friction. Friction within a fluid (water) due to
  cohesive forces.
interspecies extrapolation model. Model used to extrapolate
  from results observed in laboratory animals to humans.
interstate carrier. Any vehicle or transport which conveys
  passengers in interstate commerce.
interstice (in-TUR-stuhz). A  very small open space in a rock
  or granular material. Also called a void or void space. Also
  see pore.
invert. The lowest point of the channel inside a pipe, conduit,
  or canal.
in vitro.  In glass; a laboratory experiment performed in  a test
  tube or other vessel.
in vitro studies. Studies of'chemical effects conducted hi
  tissues, cells or subcellular extracts from an organism (i.e.,
  not in the living organsm).
in vivo. With  hi a living organism; a laboratory experiment
  performed in which the substance under study is inserted
  into a living organism.
in vivo studies. Studies of chemical effects conducted hi
  intact living organisms.

                                              Drinking Water Glossary
ion. An electrically charged atom, radical (such as S042-), or
  molecule formed by the loss or gain of one or more
ionic concentration. The concentration of any ion in solu-
  tion, usually expressed in moles per liter.
ionization (EYE-on-uh-ZAY-shun). The splitting or
  dissociation (separation) of molecules into negatively and
  positively charged ions.
irreversible effect. Effect characterized by the inability of
  the body to partially or fully repair injury caused by a toxic
jar test. A laboratory procedure that simulates a water
  treatment plant's coagulation/flocculation units with
  differing chemical doses and also energy of rapid mix,
  energy of slow mix, and settling time. The purpose of this
  procedure is to ESTIMATE the minimum or ideal coagu-
  lant dose required to achieve certain water quality goals.
  Samples of water to be treated are commonly placed in six
  jars. Various amounts of chemicals are added to each jar,
  stirred and the settling of solids is observed. The dose of
  chemicals that provides satisfactory settling removal of
  turbidity and/or color is the dose used to treat the water
  being taken into the plant at that time. When evaluating the
  results of a jar test, the operator should also consider the
  floe quality in the flocculation area and the floe loading on
  the filter.
jogging. The frequent starting and stopping of an electric
joule (jewel). A measure of energy, work or quantity of heat.
  One joule is  the work done when the point of application of
  a force of one newton is displaced a distance of one meter
  in the direction of force.


kilo. 1) Kilogram. 2) Kilometer. 3) A prefix meaning
  "thousand" used in the metric system and other scientific
  systems  of measurement.
kinetic energy. Energy possessed by a moving body of
  matter, such as water, as  a result of its motion.
kjeldahl nitrogen (KELL-doll). Nitrogen in the form of
  organic proteins or their decomposition product ammonia,
  as measured by the Kjeldahl Method.
landfill.  Facility in which solid waste from municipal and/or
  industrial sources is disposed; sanitary landfills are those
  that are operated in accordance with environmental protec-
  tion standards.
Langelier index(L.L) An index reflecting the equilibrium pH
  of a water with respect to calcium and alkalinity. This index
  is used in stabilizing water to control both corrosion and the
  deposition of scale.
Langelier index   = pH - pHs
where pH = actual pH of the water, and pHs = pH at which
  the water having the same alkalinity and calcium content is
  just saturated with calcium carbonate.
large water system. A water system that serves more than
  50,000 persons
latency. Time from the first exposure to a chemical until the
  appearance of a toxic effect.
laundering weir (LAWN-der-ing weer). Sedimentation
  basin overflow weir. A plate with V-notches along the top
  to assure a uniform flow rate and avoid short-circuiting.
launders (LAWN-ders). Sedimentation basin and filter
  discharge channels, consisting of overflow weir plates (in
  sedimentation basins) and conveying troughs.
LC50. The concentration of a chemical in air or water which
  is expected to cause death in 50% of test animals living in
  that air or water.
LD50. The dose  of a chemical taken by mouth or absorbed by
  the skin which  is expected to cause death in 50% of the test
  animals so treated.
leachate. A liquid that results from water collecting contami-
  nants as it trickles through wastes, agricultural pesticides or
  fertilizers. Leaching may occur in farming areas, feedlots,
  and landfills, and may result in hazardous substances
  entering surface water, ground water, or soil.
leaching.  The process by which soluble substances are
  dissolved and transported down through the soil by re-
lead (Pb). A heavy metal that is hazardous to health if
  breathed or swallowed. Its use in gasoline, paints, and
  plumbing compounds has been sharply restricted or
  eliminated by federal laws and regulations. See heavy
lead service line. A serice line made of lead which connects
  the water main  to the building inlet and any lead pigtail,
  gooseneck or other fitting which is connected to such lead
legionella. A  genus of bacteria, some species of which have
  caused a type of pneumonia called Legionnaires Disease.
lesion. A pathological or traumatic discontinuity of tissue or
  loss of function of a part.
lethal. Deadly; fatal.
level controls. A float device (or pressure switch) which
  senses changes in a measured variable and opens or closes a
  switch in response to that change. In its simplest form, mis
  control might be a floating ball connected mechanically to a
  switch or valve such as is used to stop water flow into a
  toilet when the tank is full.
lifetime exposure. Total amount of exposure to a substance
  that a human would receive in a lifetime (usually assumed

                                            Drinking Water Glossary
 to be 70 years).
Hndane (LYNN-dane). A pesticide that causes adverse
 health effects in domestic water supplies and also is toxic to
 freshwater and marine aquatic life.
linearity (LYNN-ee-AlR-it-ee). How closely an instrument
 measures actual values of a variable through its effective
 range; a measure used to determine the accuracy of an
linearized multistage model. Derivation of the multistage
 model, where the data are assumed to be linear at low
littoral zone (LIT-or-al). 1) That portion of a body of fresh
 water extending from the shoreline lakeward to the limit of
 occupancy of rooted plants. 2) The strip of land along the
 shoreline between the high and low water levels.
loading. The quantity of a substance entering the environ-
 ment (soil, water, or air).
LOAEL. Lowest-observed-adverse-effect level; the lowest
 dose in an experiment which produced an observable
 adverse effect.
logarithm (LOG-a-rith-m). The exponent that indicates the
 power to which a number must be raised to produce a given
 number. For example: if B2 = N, the 2 is the logarithm of N
 (to the base B), or 102 = 100 and log,0100 = 2. Also
 abbreviated to "log."

macroscopic organisms (MACK-row-SKAWP-ick).
  Organisms big enough to be seen by the eye without the aid
  of a microscope.
malignant. Very dangerous or virulent, causing or likely to
  cause death.
managerial controls. Methods of nonpoint source pollution
  control that are derived from managerial decisions, such as
  changes in applicaiton times or rates for agrochemicals.
manifold. A large pipe to which a series of smaller pipes are
  connected. Also called a HEADER.
man-made beta particle and photon emitters. All radionu-
  clides emitting beta particles and/or photons listed in
  Maximum Permissible Body Burdens and Maximum
  Permissible Concentration of Radionuclides in Air or Water
  for Occupational Exposure, NBS Handbook 69, except the
  daughter products of thorium-232, uranium-235 and
manometer (man-NAH-mut-ter). An instrument for
  measuring pressure. Usually, a manometer is a glass tube
  filled with a liquid that is used to measure ths difference in
  pressure across a flow-measuring device such as an orifice
  or Venturi meter. The instrument used to measure blood
  pressure is a type of manometer.
 margin of safety (MOS). Maximum amount of exposure
  producing no measurable effect in animals (or studied
  humans) divided by the actual amount of human exposure
 in a population.
mathematical model. Model used during risk assessment to
 perform extrapolations.
maximum contaminant level (MCL). The maximum
 permissible level of a contaminant in water which is
 delivered to the free flowing outlet of the ultimate user of a
 public water system, except in the case of turbidity where
 the maximum permissible level is measured at the point of
 entry to the distribution system. Contaminants added to the
 water under circumstances controlled by the user are
 excluded from this definition, except those contaminants
 resulting from the corrosion of piping and plumbing caused
 by water quality.
maximum contaminant level goal (MCLG). The maximum
 level of a contaminant in drinking water at which no known
 or anticipated adverse effect on the health of persons would
 occur, and which allows an adequate margin of safety.
 Maximum contaminant level goals are nonenforceable
 health goals.
maximum total trihalomethane potential (MTTP). The
 maximum concentration of total trihalomethanes produced
  ina given water containing a disinfectant residual, after 7
  days at 25 degrees C or above.
MBAS. Methylene - Blue - Active Substances.  These
  substances are used in surfactants or detergents.
MCL. See maximum contammant level.
measured variable. A characteristic or component part that
  is sensed and quantified (reduced to a reading of some kind)
  by a primary element or sensor.
Mechanical joint. A flexible device that joins pipes or
  fittings together by the use of lugs and bolts.
medium-size water system. A water  system that serves
  greater than 3,300 and less than or equal to 50,000 person.
meg. A procedure used for checking the insulation resistance
  on motors, feeders, buss bar systems, grounds, and branch
  circuit wiring. Also see megger.
megger (from megohm). An instrument used for checking
  the insulation resistance on motors,  feeders, buss bar
  systems, grounds, and branch circuit wiring. Also see MEG.
megohm. Meg means one million, so 5 megohms means 5
  million ohms. A megger reads in millions of ohms.
meniscus (meh-NlS-cuss). The curved top of a column of
  liquid (water, oil, mercury) in a small tube. When the liquid
  wets the sides of the container (as with water), the curve
  forms a valley. When the confining sides are not wetted  (as
  with mercury), the curve forms a hill or upward bulge.
 mesh. One of the openings or spaces  in a screen or woven
  fabric. The value of the mesh is usually given as the number
  of openings per inch. This value does not consider the
  diameter of the wire or fabric; therefore, the mesh number
  does not always have a definite relationship to the size of
  the hole.
 mesotrophic (MESS-o-TRO-fick). Reservoirs and lakes

                                             Drinking Water Glossary
  which contain moderate quantities of nutrients and are
  moderately productive in terms of aquatic animal and plant
metabolism (meh-TAB-uh-LIZ-um). The sum of the
  chemical reactions occurring within a cell or a whole
  organism; includes the energy-releasing breakdown of
  molecules (catabolism) and the synthesis of new molecules
metabolite. Any product of metabolism, especially a trans-
  formed chemical.
metalimnion (MET-uh-LlM-knee-on). The middle layer in
  a thermally stratified lake or reservoir. In this layer there is
  a rapid decrease in temperature with depth. Also called the
metastatic. Pertaining to the transfer of disease from one
  organ or part to another not directly connected with it.
methoxychlor (meth-OXY-klor). A pesticide which causes
  adverse health effects in domestic water supplies and is also
  toxic to freshwater and marine aquatic life.  The chemical
  name for methoxychlor is 2,2-bis (p-methoxyphenol)-1,1,1-
methyl orange alkalinity. A measure of the total alkalinity  in
  a water sample. The alkalinity is measured by the amount of
  standard sulfuric acid required to lower the pH of the water
  to a pH level of 4.5, as indicated by the change in color of
  methyl orange from orange to pink. Methyl orange alkalin-
  ity is expressed as milligrams per liter equivalent calcium
mg/L.  See milligrams per liter.
microbial growth (my-KROW-bee-ul). The activity and
  growth of microorganisms such as bacteria, algae, diatoms,
  plankton and fungi.
microgram (jig). One-millionth of a gram (3.5 x 10-8oz. =
  0.000000035 oz.).
micrograms per liter ftig/L). One microgram of a substance
  dissolved in each liter of water. This unit is equal to parts
  per billion (ppb) since one liter of water is equal hi weight
  to one billion micrograms.
micron (MY-kron). A unit of length. One millionth of a
  meter or one thousandth of a millimeter. One micron equals
  0.00004 of an inch.
microorganisms (MY-crow-OR-gan-IS-zums). Living
  organisms that can be seen individually only with the aid of
  a microscope.
mil. A  unit of length equal to 0.001 of an inch. The diameter
  of wires and tubing is measured in mils, as is the thickness
  of plastic sheeting.
milligram (rag). One-thousandth of a gram (3.5 x 10'5 oz. =
  0.000035 oz.).
milligrams per liter (mg/L). A measure of concentration of
  a dissolved substance. A concentration of one mg/L means
  that one milligram of a substance is dissolved hi each liter
  of water. For practical purposes, this unit is equal to parts
  per million (ppm) since one liter of water is equal in weight
  to one million milligrams. Thus a liter of water contining 10
  milligrams of calcium has 10 parts of calcium per one
  million parts of water, or 10 parts per million (10 ppm).
millimicron (MlLL-uh-MY-kron). A unit of length equal to
  10'3 microns (one thousandth of a micron), 10"6 millimeters,
  or 10'9 meters; correctly called a nanometer, nm.
Million-gallons Per Day (MGD). A measure of water flow.
mineralization.  The microbial conversion of an element
  from an organic to an inorganic state.
modeling. Use of mathematical equations to simulate and
  predict real events and processes.
molar or molarity. A molar solution consists of one gram
  molecular weight of a compound dissolved hi enough water
  to make one liter of solution. A gram molecular weight is
  the molecular weight of a compound hi grams. For ex-
  ample, the molecular weight of sulfuric acid (H2S04) is 98.
  A one M solution of sulfuric acid would consist of 98 grams
  of H2S04 dissolved hi enough distilled water to make one
  liter of solution.
mole. The molecular weight of a substance, usually expressed
  in grams.
molecular weight. The molecular weight of a compound hi
  grams is the sum of the atomic weights of the elements hi
  the compound. The molecular weight of sulfuric acid
  (H2S04) in grams is 98.
Element  Atomic Weight     Number of Atoms    Molecular Weight
  H            12              2
  S            32              1              32
  O            16             4              64
molecule (MOLL-uh-KULE). The smallest division of a
  compound that still retains or exhibits all the properties of
  the substance.
monitoring. Measuring concentrations of substances hi
  environmental media or hi human or other biological
monomer (MON-o-MER). A molecule of low molecular
  weight capable of reacting with identical or different
  monomers to form polymers.
monomictic (mo-no-MlCK-tick). Lakes and reservoirs
  which are relatively deep, do not freeze over during the
  whiter months, and undergo a single stratification and
  mixing cycle during the year. These lakes and reservoirs
  usually become destratified during the mixing cycle, usually
  in the fall of the year.
monovalent. Having a valence of one,  such as the cuprous
  (copper) ion, Cu+.
mortality. Death.
MOS.  See margin of safety.
most probable number (MPN). MPN is the Most Probable
  Number of coliform-group organisms per unit volume of
  sample water. Expressed as the number of organisms per

                                            Drinking Water Glossary
  100 mL of sample water.
motile (MO-till). Capable of self-propelled movement. A
  term that is sometimes used to distinguish between certain
  types of organisms found in water.
monitoring wells.  Wells used to collect ground-water
  samples for analysis to determine the amount, type, and
  spread of contaminants in ground water.
motor efficiency. The ratio of energy delivered by a motor to
  the energy supplied to it during a fixed period or cycle.
  Motor efficiency ratings will vary depending upon motor
  manufacturer and usually will range from 88.9 to 90.0
MPN. See most probable number.
MTD. Maximum tolerated dose, the dose that an animal
  species can tolerate for a major portion of its lifetime
  without significant impairment or toxic effect other than
mudballs. Material that is approximately round in shape and
  varies from pea-sized up to two or more inches in diameter.
  This material forms in filters and gradually increases in size
  when not removed by the backwashing process.
mulch.  Any substance spread or allowed to remain on the
  soil surface to conserve soil moisture and shield soil
  particles from the erosive forces of raindrops and runoff.
multi-stage pump. A pump that has more than one impeller.
  A single-stage pump has one impeller.
multiple use. Use of land for more than one purpose; i.e.,
  grazing of livestock, wildlife production, recreation,
  watershed, and timber production. Could also apply to  use
  of bodies of water for recreational purposes, fishing, and
  water supply.
multistage model. Mathematical model based on the
  multistage theory of the carcinogenic process, which yields
  risk estimates either equal to or less than the one-hit model.
municipal sewage. Wastes (mostly liquid) originating from
  a community; may be composed of domestic wastewaters
  and/or industrial wastewaters.
mutagen. An agent that causes a permanent geetic change in
  a cell other than that which occurs during normal genetic
mutagenicity. The capacity of a chemical or physical agent
  to cause permanent alteration of the genetic material within
  living cells.

 N. See normal.
 National Environmental Training Association (NETA). A
  professional organization devoted to serving the environ-
  mental trainer and promoting better operation of water-
  works and pollution control facilities. For information on
  NETA membership and publications, contact NETA, 8687
  Via de Ventura, Suite 214, Scottsdale, AZ 85258.
National Institute of Occupational Safety and Health. See
National Interim Primary Drinking Water Regulations.
  Commonly referred to as NIPDWRs.
National Pollutant Discharge. Elimination System permit is
  the regulatory agency document issued by either a federal
  or state agency which is designed to control all discharges
  of pollutants from point sources in U.S. waterways. NPDES
  permits regulate discharges into navigable waters from all
  point sources of pollution, including industries, municipal
  treatment plants, large agricultural feed lots and return
  Irrigation flows.
National Secondary Drinking Water Regulations. Com-
  monly referred to as NSDWRs.
NCWS.  See non-community water system.
near the first service connection. At one of the 20 percent
  of all service connections in the entire system that are
  nearest the water supply treatment facility, as measured by
  water transport time within the distribution system.
necrosis. Death of cells or tissue.
nematodes.  Roundworms, any of which are pathogenic for
  plants and sometimes animals.
nephelometric (NEFF-el-o-MET-rick). A means of
  measuring turbidity in a sample by using an instrument
  called a nephelometer. A nephelometer passes light through
  a sample and the amount of light deflected (usually at a 90-
  degree angle) is then measured.
neoplasm. An abnormal growth or tissue, as a tumor.
nephelometric turbidity unit (NTU). The unit of measure
  for turbidity.
NETA. See National Environmental Training Association.
neurotoxicity. Exerting a destructive or poisonous effect on
  nerve tissue.
newton. A force which, when applied to a body having a
  mass of one kilogram, gives it an acceleration of one meter
  per second per second.
NIOSH. The National Institute of Occupational Safety and
  Health is an organization that tests and approves safety
  equipment for particular applications. NIOSH is the
  primary Federal agency engaged in research in the national
  effort to eliminate on-the-job hazards to the health and
  safety of working people. The NIOSH Publications Catalog
  contains a listing of NIOSH publications mainly on
  industrial hygiene and occupational health. To obtain a copy
  of the catalog, write to National Technical Information
  Service (NTIS), 5285 Port Royal Road, Springfield, VA
  22161. NTIS Stock No. PB-86-116-787, price $45.95.
NIPDWR. National Interim Primary Drinking Water
nitrification. The biochemical transformation of ammonium
  nitrogen to nitrate nitrogen.
nitrification inhibitor.  A chemical that slows down the

                                             Drinking Water Glossary
  conversion of ammonium to nitrate nitrogen.
nitrogen fixation.  The biological or chemical process by
  which elemental nitrogen, from the air, is converted to
  organic or available nitrogen.                       |tft
nitrogenous (nye-TRAH-jen-us). A term used to describe
  chemical compounds (usually organic) containing nitrogen
  in combined forms. Proteins and nitrates are nitrogenous
NOAEL. No-observed-adverse-effect level; the highest dose
  in an experiment which did not produce an observable
  adverse effect.
noble metal. Chemically inactive metal (such as gold). A
  metal that does not corrode easily and is much scarcer (and
  more valuable) than the so-called useful or base metals.
  Also see base metal.
NOEL. No-observed-effect level; dose level at which no
  effects are noted.
nominal diameter. An approximate measurement of the
  diameter of a pipe. Although the nominal diameter is used
  to describe the size or diameter of a pipe, it is usually not
  the exact inside diameter of the pipe.
non-community water system (NCWS). A public water
  system that is not a community water system.  There are
  two types of NCWSs: transient and non-transient.
non-conventional pollutant. Any pollutant which is not a
  statutorly listed or which is poorly understood by the
  scientific community.
non-ionic polymer (NON-eye-ON-ick). A polymer that has
  no net electrical charge.
non-point source. Pollution sources which are diffuse and do
  not have a single point of origin or are not introduced into a
  receiving stream from a specific outlet. The pollutants are
  generally carried off the land by stormwater runoff. The
  commonly used categories for non-point sources are:
  agriculture, forestry, urban, mining, construction, dams and
  channels, land disposal, and saltwater intrusion.
non-potable (non-POE-tuh-buIl). Water that may contain
  objectionable pollution, contamination, minerals, or
  infective agents and is considered unsafe and/or unpalatable
  for drinking.
non-transient non-community water system (NTNCWS).
  A public water  system that regularly serves at least 25 of
  the same nonresident persons per day for more than six
  months per year.
normal. A normal solution contains one gram equivalent
  weight of reactant (compound) per liter of solution. The
  equivalent weight of an acid is that weight which contains
  one gram atom of ionizable hydrogen or its chemical
  equivalent. For example, the equivalent weight of sulfuric
  acid (H2S04) is 49 (98 divided by 2 because there are two
  replaceable hydrogen ions). A one N solution of sulfuric
  acid would consist of 49 grams of H2S04 dissolved in
  enough water to make one liter of solution.
NPL. National Priorities List; a list of Superfund sites
  chosen for immediate attention.
NSDWR. National Secondary Drinking Water Regulations.
NTNCWS. See non-transient non-community water system.
NTP. National Toxicology Program.
nutrient. Any substance that is assimilated (taken in) by
  organisms and promotes growth. Nitrogen and phosphorous
  are nutrients which promote the growth of algae. There are
  other essential and trace elements which are also considered
nutrient pollution.  Contamination of water resources by
  excessive inputs of nutrients; insurface waters, excess  algal
  production is a major concern.


Occupational Safety and Health Act of 1970. See OSHA.
odor threshold. The minimum odor of a water sample that
  can just be detected after successive dilutions with odorless
  water. Also called THRESHOLD ODOR.
offstream uses. Water withdrawn from surface or groundwa-
  ter sources for use at another place.
offset (or DROOP). The difference between the actual value
  and the desired value (or set point); characteristic of
  proportional controllers that do not incorporate reset action.
OHM. The unit of electrical resistance. The resistance of a
  conductor in which one volt produces a current of one
olfactory fatigue(oh-FAK-tore-ee). A condition in which a
  person's nose, after exposure to certain odors, is no longer
  able to detect the odor.
oligotrophic (AH-lig-o-TRO-fick). Reservoirs and lakes
  which are nutrient poor and contain little aquatic plant or
  animal life.
oncology.  Study of cancer.
one-hit model. Mathematical model based on the biological
  theory that a single "hit" of some minimum critical amount
  of a carcinogen at a cellular target- namely, DNA-can
  initiate an irreversible series of events, eventually  leading to
  a tumor.
optimal corrosion control treatment. The corrosion control
  treatment that minimizes the lead and copper concentrations
  at users' taps while insuring that the treatment does not
  cause the water system to violate any national primary
  drinking water regulations.
operation and maintenance costs. The ongoing, repetitive
  costs of operating a water system; for example, employee
  wages and costs for treatment chemicals and periodic
  equipment repairs.
oral. Of the mouth; through or by the mouth.
organic. Substances that come from animal or plant sources.
  Organic substances always contain carbon. (Inorganic
  materials are chemical substances of mineral origin.) Also

                                             Drinking Water Glossary
  see inorganic
organics. 1) A term used to refer to chemical compounds
  made from carbon molecules. These compounds may be
  natural materials (such as animal or plant sources) or man-
  made materials (such as synthetic organics). Also see
  organic. 2) Any form of animal or plant life. Also see
organism. Any form of animal or plant life. Also see
orifice(OR-uh-fiss). An opening (hole) in a plate, wall or
  partition An orifice flange or plate placed in a pipe consists
  of a slot or a calibrated circular hole smaller than the pipe
  diameter. The difference in pressure in the pipe above and
  at the orifice may be used to determine the flow in the pipe.
ORP. Oxidation-Reduction Potential. The electrical potential
  required to transfer electrons from one compound or
  element (the oxidant) to another compound or element (the
  reductant); used as a qualitative measure of the state of
  oxidation in water treatment systems.
orthotolidine (or-tho-TOL-uh-dine). Orthotolidine is a
  colorimetric indicator of chlorine residual. If chlorine is
  present, a yellow-colored compound is produced. This
  reagent is no longer approved for chemical analysis.
OSHA (O-shuh). The Williams-Steiger Occupational Safety
  and Health Act of 1970 (OSHA) is  a law designed to
  protect the health and safety of industrial workers and also
  the operators of water supply systems and treatment plants.
  OSHA also refers to the federal and state agencies which
  administrator the OSHA regulations.
osmosis (oz-MOE-sis). The passage  of a liquid from a weak
  solution to a more concentrated solution across a semiper-
  meable membrane. The membrane  allows the passage of
  the solvent (water) but not the dissolved solids (solutes).
  This process tends to equalize the conditions on either side
  of the membrane.
overall efficiency pump. The combined efficiency of a pump
  and motor together. Also called the WIRE-TO-WATER
overdraft The pumping of water from a groundwater basin
  or aquifer in excess of the supply flowing into the basin.
  This pumping results in a depletion or "mining" of the
  groundwater in the basin.
overflow rate. One of the guidelines for the design of settling
  tanks and clarifiers in treatment plants. Used by operators to
  determine if tanks and clarifiers are hydraulically (flow)
  over- or underloaded. Also called SURFACE LOADING.
Overflow Rate (GDP/sq ft) = Flow (GPD)/Surface Area (sq ft)
overturn. The almost spontaneous mixing of all layers of
  water in a reservoir or lake when the water temperature
  becomes similar from top to bottom. This may occur in the
  fall/winter when the surface waters cool to the same
  temperature as the bottom waters and also in the spring
  when the surface waters warm after the ice melts.
oxidation (ox-uh-DAY-shun). Oxidation is the addition of
  oxygen, removal of hydrogen, or the removal of electrons
  from an element or compound. In the environment, organic
  matter is oxidized to more stable substances. The opposite
  of reduction
oxidation-reduction potential. The electrical potential
  required to transfer electrons from one compound or
  element (the oxidant) to another compound or element (the
  reductant); used as a qualitative measure of the state of
  oxidation in water treatment systems.
oxidizing agent. Any substance, such as oxygen (O2) or
  chlorine (C12), that will readily add (take on) electrons. The
  opposite is a reducing agent.
ozonation (O-zoe-NAY-shun). The application of ozone to
  water for disinfection or for taste and odor control.
packed tower aeration. A method of treating water to
  remove volatile organic chemical (VOCs) contaminants.
  As water is mixed with air, VOCs move from water to air
  which then passes through carbon filters to trap the con-
palatable (PAL-a-ta-ble). Water at a desirable temperature
  that is free from objectionable tastes, odors, colors, and
  turbidity. Pleasing to the senses.
parshall flume. A device used to measure the flow in an
  open channel. The flume narrows to a throat of fixed
  dimensions and then expands again. The rate of flow can be
  calculated by measuring the difference in head (pressure)
  before and at the throat of the flume.
particle count. The results of a microscopic examination of
  treated water with a special "particle counter" which
  classifies suspended particles by number and size.
particulate (par-TICK-you-let). A very small solid sus-
  pended in water which can vary widely in size, shape,
  density, and electrical charge. Colloidal and dispersed
  particulates are artificially gathered together by the pro-
  cesses of coagulation and flocculation.
partition coefficient.  A measure of the extent to which a
  pesticide is divided between the soil and ater phases.
parts per million (PPM). Parts per million parts, a measure-
  ment of concentration on a weight or volume basis. This
  term is equivalent to milligrams per liter (mg/L) which is
  the preferred term.
pascal. The pressure or stress of one newton per square
  meter. (Abbreviated Pa)
  1 psi = 6895 Pa = 6.895 kN/sq m = 0.0703 kg/sq cm
pathogenic organisms (path-o-JEN-ick). Organisms,
  including bacteria, viruses or cysts, capable of causing
  diseases (typhoid, cholera, dysentery) hi a host (such as a
  person). There are many types of organisms which do NOT
  cause disease. These organisms are called non-pathogenic.
 pathogens. Microorganisms that can cause disease in other

                                              Drinking Water Glossary
  organisms or in humans, animals and plants. They may be
  bacteria, viruses, or parasites and are found in sewage, in
  runoff from animal farms or rural areas populated with
  domestic and/or wild animals, and in water used for
  swimming. Fish and shellfish contaminated by pathogens,
  or the contaminated water itself, can cause serious illnesses.
pathology. The study of disease.
percent saturation. The amount of a substance that is
  dissolved in a solution compared with the amount that could
  be dissolved hi the solution, expressed as a percent.
Amount of substance that is dissolved  x 100%
Amount that could be dissolved in solution
percolating water (PURR-co-LAY-ting). Water that passes
  through soil or rocks under the force of gravity.
percolation (PURR-ko-LAY-shun).  1) The slow seepage of
  water into and through the ground. 2) The slow passage of
  water through a filter medium.
performance evaluation sample. A reference sample
  provided to a laboratory for the purpose of demonstrating
  that the laboratory can successfully analyze the sample
  within limits of performance specified by the Agency. The
  true value of the concentration of the reference material is
  unknown to the laboratory at the time of the analysis.
periphyton (puh-RIF-uh-tawn). Microscopic plants and
  animals that are firmly attached to solid surfaces under
  water such as rocks, logs, pilings and other structures.
permeability. Generally used to refer to the ability of rock or
  soil to transmit water.
permeate (PURR-me-ate). To penetrate and pass through, as
  water penetrates and passes through soil and other porous
permissible dose. The dose of a chemical that may be
  received by an individual without the expectation of a
  significantly harmful result.
persistence. The resistance to degradation as measured by
  the period of tune required for complete decomposition of
  a material.
person. An individual, corporation, company, association,
  partnership; municipality; or State, Federal, or tribal
pesticide. Any substance or chemical  designed or formulated
  to kill or control weeds or animal pests. Also see algicide,
  herbicide, insecticide and rodenticide.
petroleum derivatives.  Chemicals formed when gasoline
  breaks down hi contact with ground water.
pH (pronounce as separate letters). pH is an expression of
  the intensify of the basic or acid condition of a liquid.
  Mathematically, pH is the logarithm (base 10) of the
  reciprocal of the hydrogen ion concentration, [H4].
        pH = Log (1/[H+])
The pH may range from 0 to 14, where 0 is most acid, 14
  most basic, and 7 neutral. Natural waters usually have a pH
  between 6.5 and 8.5.
 pharmacokinetics. The dynamic behavior of chemicals
  inside biological systems; it includes the processes of
  uptake, distribution, metabolism, and excretion.
 phenolic compounds (FEE-nolI-LICK). Organic com-
  pounds that are derivatives of benzene.
 phenolphthalein alkalinity (FEE-nol-THAY-leen). The
  alkalinity hi a water sample measured by the amount of
  standard acid required to lower the pH to a level of 8.3, as
  indicated by the change in color of phenolphthalein from
  pink to clear. Phenolphthalein alkalinity is expressed as
  milligrams per liter equivalent calcium carbonate.
 photosynthesis (foe-tow-SIN-thuh-sis). A process in which
  organisms, with the aid of chlorophyll (green plant en-
  zyme), convert carbon dioxide and inorganic substances
  into oxygen and additional plant material, using sunlight for
  energy. All green plants grow by this process.
 phytoplankton (Flo-tow-PANK-ton). Small, usually
  microscopic plants (such as algae), found in lakes, reser-
  voirs, and other bodies of water.
 pico. A prefix used in the metric system and other scientific
  systems of measurement which means 10'12 or
 picocurie (pCi). A measure of radioactivity. One picocurie of
  radioactivity is equivalent to 0.037 nuclear disintegrations
  per second.
 plan view. A diagram or photo showing a facility as  it would
  appear when looking down on top of it.
 plankton. 1) Small, usually microscopic, plants (phytoplank-
  ton) and animals (zooplankton) in aquatic systems. 2) All of
  the smaller floating, suspended or self-propelled  organisms
  hi a body of water.
plug flow. A type of flow that occurs hi tanks, basins or
  reactors when a slug of water moves through a tank without
  ever dispersing or mixing with the rest of the water flowing
  through the tank.
plumes. The way polluted water extends downstream from
  the pollution source (analogous to smoke from a  smoke-
  stack as it drifts downwind hi the atmosphere).
point of disinfectant application. The point where disinfec-
  tant is applied and water downstream of that point is not
  subject to recontamination by surface water runoff.
point-of-entry treatment device. A treatment device applied
  to the drinking water entering a house or building for the
  purpose of reducing contaminants hi the drinking water
  distributed throughout the house or building .
point-of-use treatment device. A treatment device applied to
  a single tap used for the purpose of reducing contaminants
  hi drinking water at that one tap.
point source. A stationery location or fixed facility from
  which pollutants are discharged or emitted. Also, any single
  identifiable source of pollution, e.g., a pipe, ditch, ship,  ore
  pit, factory smokestack.

                                             Drinking Water Glossary
pole shader. A copper bar circling the laminated iron core
  inside the coil of a magnetic starter.
pollutant. Generally, any substance introduced into the
  environment that adversely affects the usefulness of a
pollution. Generally, the presence of matter or energy whose
  nature, location or quantity produces undesired environmen-
  tal effects. Under the Clean Water Act, for example, the
  term is defined as the man-made or man-induced alteration
  of the physical, biological, and radiological integrity of
polyclectrolyte (POLLY-ee-LECK-tro-lite). A high-
  molecular-weight (relatively heavy) substance having points
  of positive or negative electrical charges that is formed by
  either natural or man-made processes. Natural polyelectro-
  lytes may be of biological origin or derived from starch
  products and cellulose derivatives. Man-made polyelectro-
  lytes consist of simple substances that have been made into
  complex substances of high molecular weight. Used with
  other chemical coagulants to aid in binding small suspended
  particles to larger chemical floes for their removal from
  water. Often called a polymer.
polymer. A chemical formed by the union of many mono-
  mers (a molecule of low molecular weight). Polymers are
  used with other chemical coagulants to aid in binding small
  suspended particles to larger chemical floes for their
  removal from water. All polyelectrolytes are polymers, but
  not all polymers are polyelectrolytes.
population at risk. A population subgroup that is more likely
  to be exposed to a chemical, or is more sensitive to a
  chemical, than is the general population.
pore. A very small open space in a rock or granular material.
  Also see interstice
porosity,  the capacity of soil of rock to hold water.
positive displacement pump. A type of piston, diaphragm,
  gear or screw pump that delivers a constant volume with
  each stroke. Positive displacement pumps are used as
  chemical solution feeders.
postchlorination. The addition of chlorine to the plant
  effluent, FOLLOWING plant treatment, for disinfection
potency. Amount of material necessary to produce a given
  level of a deleterious effect.
potcntiation. The effect of one chemical to increase the
  effect of another chemical.
potentiometric surface. The level to which water will rise in
  cased wells or other cased excavations into aquifers,
  measured as feet above mean sea level.
potable water. Water that is safe and satisfactory for
  drinking and cooking.
power factor. The ratio of the true power passing thrugh an
  electric circuit to the product of the voltage and amperage
  in the circuit. This is a measure of the lag or load of the
  current with respect to the voltage.
ppb. Parts per billion. Also ng/L or micrograms per liter.
ppm. Parts per million. Also mg/L or milligrams per liter.
prechlorination. The addition of chlorine at the headworks
  of the plant PRIOR TO other treatment processes mainly
  for disinfection and control of tastes, odors and aquatic
  growths. Also applied to aid hi coagulation and settling.
precipitate (pre-SlP-uh-TATE). 1) An insoluble, finely
  divided substance which is a product of a chemical reaction
  within a liquid. 2) The separation from solution of an
  insoluble substance.
precipitation (pre-SlP-uh-TAY-shun). 1) The process by
  which atmospheric moisture falls onto a land or water
  surface as rain, snow, hail, or other forms of moisture. 2)
  The chemical transformation of a substance hi solution into
  an insoluble form (precipitate).
precision. The ability of an instrument to measure a process
  variable and to repeatedly obtain the same result. The
  ability of an instrument to reproduce the same results.
precursor, THM (pre-CURSE-or). Natural organic com-
  pounds found in all surface and groundwaters. These
  compounds MAY react with halogens (such as chlorine) to
  form trihalomethanes (try-HAL-o-METH-hanes) (THMs);
  they MUST be present hi order for THMs to form.
prescriptive (pre-SKRIP-tive). Water rights which are
  acquired by diverting water and putting it to use hi accor-
  dance with specified procedures. These procedures include
  filing a request to use unused water hi a stream, river or
  lake with a state agency.
pressure control. A switch which operates on changes hi
  pressure. Usually this is a diaphragm pressing against a
  spring. When the force on the diaphragm overcomes the
  spring pressure, the switch is actuated (activated).
pressure head. The vertical distance (hi feet) equal to the
  pressure (hi psi) at a specific point. The pressure head is
  equal to the pressure hi psi tunes 2.31 fi/psi.
prevalence study. An epidemiological study which examines
  the relationships between diseases and exposures as they
  exist hi a defined population at a particular point hi tune.
primacy. The responsibility for ensuring that a law is
  implemented, and the authority to enforce a law and related
  regulations. A primacy agency has the primary responsibil-
  ity for administrating and enforcing regulations.
primary element. An instrument which measures (senses) a
  physical condition or variable of interest. Floats and
  thermocouples are examples of primary elements. Also
  called a sensor.
prime. The action of filling a pump casing with water to
  remove the air. Most pumps must be pruned before startup
  or they will not pump any water.
prior appropriation. A doctrine of water law that allocates
  the right to use water on a first-come first-serve basis.
process variable. A physical or chemical quantity which is

                                              Drinking Water Glossary
  usually measured and controlled in the operation of a water
  treatment plant or an industrial plant.
product water. Water that has passed through a water
  treatment plant. All the treatment processes are completed
  or finished. This water is the product from the water
  treatment plant and is ready to be delivered to the consum-
  ers. Also called finished water.
profile. A drawing showing elevation plotted against dis-
  tance, such as the vertical section or side view of a pipeline.
prospective study. An epidemiological study which exam-
  ines the development of disease in a group of persons
  determined to be presently free of the disease.
Prussian blue. A blue paste or liquid (often on a paper like
  carbon paper) used to show a contact area. Used to deter-
  mine if gate valve seats fit properly.
PSIG. Pounds per Square Inch Gage pressure. The pressure
  within a closed container or pipe measured with a gage in
  pounds per square inch. See gage pressure.
public water system. A system for the provision to the
  public of piped water for human consumption, If such
  system has at least fifteen service connections or regularly
  serves an average of at least twenty-five individuals daily at
  least 60 days out of the year. Such term includes: 1) any
  collection, treatment, storage, and distribution facilities
  under control of the operator of such system and used
  primarily in connection with such system, and 2) any
  collecton or pretreatment storage facilities not under such
  control which are used primarily in connection with such
  system. A public water system is either a "community water
  system" or a "non-community water system."
pumping station. Mechanical devices installed in sewer or
  water  systems or other liquid-carrying pipelines that move
  the liquids to a higher level.
pumping water level. The vertical distance in feet from the
  centerline of the pump discharge to the level of the free
  pool while water is being drawn from the pool.
purveyor, water (purr-VAY-or). An agency or person that
  supplies water (usually potable water).
putrefaction (PEW-truh-FACK-shun). Biological decom-
  position of organic matter, with the production of ill-
  smelling and tasting products, associated with anaerobic (no
  oxygen present) conditions.

qualitative. Descriptive of kind, type or direction, as opposed
  to size, magnitude or degree.
quantitative. Descriptive of size, magnitude or degree.
quicklime. A material that is mostly calcium oxide (CaO) or
  calcium oxide in natural association with a lesser amount of
  magnesium oxide. Quicklime is capable of combining with
  water to form hydrated lime. Also see hydrated lime.
radial to impeller. Perpendicular to the impeller shaft.
  Material being pumped flows at a right angle to the impel-
radical. A group of atoms that is capable of remaining
  unchanged during a series of chemical reactions. Such
  combinations (radicals) exist in the molecules of many
  organic compounds; sulfate (SO42') is an inorganic radical.
radionuclide. Any man-made or natural element which emits
  radiation in the form of alpha or beta particles, or as gamma
range. The spread from minimum to maximum values that an
  instrument is designed to measure. Also see span and
  effective range.
ranney collector. This water collector is constructed as a dug
  well from  12 to  16 feet (3.5 to 5 m) in diameter that has
  been sunk as a caisson near the bank of a river or lake.
  Screens are driven radially and approximately horizontally
  from this well into the sand and the gravel deposits underly-
  ing the river.
raw water.  1) Water in its natural state, prior to any treat-
  ment. 2) Usually the water entering the first treatment
  process of a water treatment plant,
reaeration (RE-air-A-shun). The introduction of air through
  forced ah- diffusers into the lower  layers of the reservoir. As
  the air bubbles form and rise through the water, oxygen
  from the air dissolves into the water and replenishes the
  dissolved oxygen. The rising bubbles also cause the lower
  waters to rise to the surface where oxygen from the
  atmosphere is transferred to the water. This is sometimes
  called surface reaeration.
reagent (re-A-gent). A pure chemical substance that is used
  to make new products or is used hi chemical tests to
  measure, detect, or examine other  substances.
recarbonation (re-CAR-bun-NAY-shun). A process in
  which carbon dioxide is bubbled into the water being
  treated to lower the pH. The pH may also be lowered by the
  addition of acid. Recarbonation is  the final stage in the
  lime-soda ash softening process. This process converts
  carbonate ions to bicarbonate ions and stabilizes the
  solution against the precipitation of carbonate compounds.
receiver. A device which indicates the result of a measure-
  ment. Most receivers in the water utility field use either a
  fixed scale and movable indicator  (pointer) such as pressure
  gage or a movable scale and movable indicator like those
  used on a circular-flow recording chart. Also called an
receiving waters. All distinct bodies of water that receive
  runoff or wastewater discharges, such as streams, rivers,
  ponds, lakes, and estuaries.
receptor. 1) In biochemistry: a specialized molecule hi a cell
  that binds a specific chemical with high specificity and high
  affinity. 2) In exposure assessment: an organism that

                                             Drinking Water Glossary
 receives, may receive, or has received environmental
 exposure to a chemical.
recharge. Process by which rain water (precipitation) seeps
 into the ground-water sysem.
recharge area. Generally, an area that is connected with the
 underground aquifer(s) by a highly porous soil or rock
 layer. Water entering a recharge area may travel for miles
recharge rate. The quantity of w.ater per unit time that
 replenishes or refills an aquifer.
recorder. A device that creates a permanent record, on a
 paper chart or magnetic tape, of the changes of some
 measured variable.
reducing agent Any substance, such as base metal (iron) or
 the sulfide ion (S20, that will readily donate (give up)
 electrons. The opposite is an oxidizing agent.
reduction (re-DUCK-shun). Reduction is the addition of
 hydrogen, removal of oxygen, or the addition of electrons to
 an element or compound. Under anaerobic conditions (no
 dissolved oxygen present), sulfur compounds are reduced to
 odor-producing hydrogen sulfide (H2S and other com-
 pounds. The opposite of oxidation.
reference. A physical or chemical quantity whose value is
 known exactly,  and thus is used to calibrate or standardize
rem. The unit of dose equivalent from ionizing radiation to
  the total body or any internal organ or organ system. A
  "millirem (mrem)" is 1/1000 of a rem.
renal. Pertaining to the kidney.
repeat compliance period. Any subsequent compliance
  period after the initial compliance period.
representative sample. A portion of material or water that is
  as nearly identical in content and consistency as possible to
  that in the larger body of material or water being sampled.
reservoir. Any natural or artificial holding area used to store;
  regulate, or control water.
residual chlorine. The amount of free and/or available
  chlorine remaining after a given contact time under speci-
  fied conditions.
residual disinfectant concentration ("C" in CT calcula-
  tions). The concentration of disinfectant measured in mg/L
  in a representative sample of water.
 residue. The dry solids remaining after the evaporation of a
  sample of water or sludge. Also see total dissolved solids
 respiration. The process in which an organism uses oxygen
  for its life processes and gives off carbon dioxide.
 retrospective study. An epidemiological study which
  compares diseased persons with non-diseased persons and
  works back in time to determine exposures.
 reverse osmosis (oz-MOE-sis). The application of pressure
  to a concentrated solution which causes the passage of a
 liquid from the concentrated solution to a weaker solution
 across a semipermeable membrane. The membrane allows
 the passage of the solvent (water) but not the dissolved
 solids (solutes). The liquid produced is a demineralized
 water. Also see osmosis.
reversible effect. An effect which is not permanent, espe-
 cially adverse effects which diminish when exposure to a
 toxic chemical is ceased.
RfD (Reference dose). The daily exposure level which,
 during an entire lifetime of a human, appears to be without
 appreciable risk on the basis of all facts known at the time.
 Same as ADI.
rill.  A small channel eroded into the soil surface by runoff;
 rills easily can be smoothed out (obliterated) by normal
riparian rights. A doctrine of state water law under which a
 land owner is entitled to use the water on or bordering his
 property, including the right to prevent diversion or misuse
 of upstream waters. Riparian land is land that borders on
 surface water.
risk. The potential for realization of unwanted adverse
  consequences or events.
risk assessment. A qualitative or quantitative evaluation of
 the environmental and/or health risk resulting from expo-
  sure to a chemical or physical agent (pollutant); combines
  exposure assessment results with toxicity assessment results
  to estimate risk.
risk characterization. Final component of risk assessment
  that involves integration of the data and analysis involved in
  hazard evaluation, dose-response evaluation, and human
  exposure evaluation to determine the likelihood that humans
  will experience any of the various forms of toxicity
  associated with a substance.
risk estimate. A description of the probability that organisms
  exposed to a specified dose of chemical will develop an
  adverse response (e.g., cancer).
risk factor. Characteristic (e.g., race, sex, age, obesity) or
  variable (e.g., smoking, occupational exposure level)
  ssociated with increased probability of a toxic effect.
risk management. Decisions about whether an assessed risk.
  is sufficiently high to present a public health concern and
  about the appropriate means for control of a risk judged to
  be significant.
 risk specific dose. The dose associated with a specified risk
 rodenticide (row-DENT-uh-SIDE). Any substance or
  chemical used to kill or control rodents.
 rotameter (RODE-uh-ME-ter). A device used to measure
  the flow rate of gases and liquids. The gas or liquid being
  measured flows vertically up a tapered, calibrated tube.
  Inside the tube is a small ball or bullet-shaped float (it may
  rotate) that rises or falls depending on the  flow rate. The
  flow rate may be read on a scale behind or on the tube by

                                               Drinking Water Glossary
   looking at the middle of the ball or at the widest part or top
   of the float.
 rotor. The rotating part of a machine. The rotor is surrounded
   by the stationary (non-moving) parts (stator) of the ma-"
 route of exposure. The avenue by which a chemical comes
   into contact with an organism (e.g., inhalation, ingestion,
   dermal contact, injection).
 run-off. That part of precipitation, snow melt, or irrigation
   water that runs off the land into streams or other surface
   water. It can carry pollutants from the ah- and land into the
   receiving waters.
 sacrificial anode. An easily corroded material deliberately
  installed in a pipe or tank. The intent of such an installation
  is to give up (sacrifice) this anode to corrosion while the
  water supply facilities remain relatively corrosion free.
 safe. Condition of exposure under which there is a "practical
  certainty" that no harm will result in exposed individuals.
 Safe Drinking Water Act (SDWA). Commonly referred to
  as SDWA. An Act passed by the U.S. Congress in 1974.
  The Act establishes a cooperative program among local,
  state and federal agencies to insure safe drinking water for
 safe water. Water that does not contain harmful bacteria, or
  toxic materials or chemicals. Water may have taste and
  odor problems, color and certain mineral problems and still
  be considered safe for drinking.
 safe yield. The annual quantity of water that can be taken
  from a source of supply over a period of years without
  depleting the source beyond its ability to be replenished
  naturally in "wet years".
 salinity. 1) The relative  concentration of dissolved salts,
  usually sodium chloride, in a given water.. 2) A measure of
  the concentration of dissolved mineral substances in water.
 sand.  Soil particles between 0.05 and 2 .0 mm hi diameter.
 sand filters. Devices that remove some suspended solids
  from sewage. Air and bacteria decompose additional wastes
  filtering through the sand so that cleaner water drains from
  the bed.
 sanitary sewer. A sewer that transports only wastewaters
  (from domestic residences and/or industries) to a wastewa-
  ter treatment plant.
 sanitary survey. An on-site review of the water source,
  facilities, equipment, operation, and maintenance of a
  public water system for the purpose of evaluating the
  adequacy of the facilities for producing and distributing safe
  drinking water.
saprophytes (SAP-row-FlGHTS). Organisms living on dead
  or decaying organic matter. They help natural decomposi-
  tion of organic matter in water.
 saturated zone. The area below the water table where all
   open spaces are filled with water.
 saturation. The condition of a liquid (water) when it has
   taken into solution the maximum possible quantity of a
   given substance at a given temperature and pressure.
 saturator (SAT-you-RAY-tore). A device which produces a
   fluoride solution for the fluoridation process. The device is
   usually a cylindrical container with granular sodium
   fluoride on the bottom. Water flows either upward or
   downward through the sodium fluoride to produce the
   fluoride solution.
 schedule, pipe. A sizing system of arbitrary numbers that
   specifies the ID. (inside diameter) and O.D. (outside
   diameter) for each diameter pipe. This term is used for
   steel, wrought iron, and some types of plastic pipe. Also
   used to describe the strength of some types of plastic pipe.
 SCD (SWCD).  Soil Conservation District (also called Soil
   and Water Conservation District in some areas); a local
   government entity with hi a defined water or soil protection
   area tat provides assistance to farmers and other local
   residents in conserving natural resources, especially soil and
 SCFM. Cubic Feet of air per Minute at Standard conditions
   of temperature, pressure and humidity (0 degrees C /14.7
   psia /50% relative humidity).
 SCS. Soil Conservation Service. An agency of the United
   States Department of Agriculture that provides technical
   assistance for resource conservation to farmers, other
   Federal, state and local agencies, and to local soil conserva-
  tion districts.
 SDWA. See Safe Drinking Water Act.
 secchi disc (SECK-key). A flat, white disc lowered into the
 , water by a rope until it is just barely visible. At this point,
  the depth of the disc from the water surface is the recorded
  Secchi disc transparency.
 seepage.  The  percolation of water through the soil from
  unlined channels, ditches, watercourses and water storage
 sedimentation. A water treatment process in which solid
  particles settle out of the water being treated hi a large
  clarifier or sedimentation basin .
 sediment yield.  The quantity of sediment arriving at a
  specific location.
 seize up. Seize up occurs when an engine overheats and a
 part expands to the point where the engine will not run.
 Also called "freezing."
 semi-confined aquifer. An aquifer that is partially confined
 by a soil layer (or layers) of low permeability through
 which recharge and discharge can occur.
sensor. An instrument that measure (senses) a physical
 condition or variable of interest. Floats and thermocouples
 are examples of sensors. Also called a primary element.
septage. The liquid and semisolid contents removed by

                                             Drinking Water Glossary
  pumping from a septic tank.
septic (SEP-tick). A condition produced by bacteria when all
  oxygen supplies are depleted. If severe, bottom deposits and
  water turn black, give off foul odors, and the water has a
  greatly increased chlorine demand.
septic system. An onsite system designed to treat and
  dispose of domestic sewage; a typical septic system consists
  of a tank that receives wastes from a residence or business
  and a system of tile lines or a pit for disposal of the liquid
  effluent that remains after decomposition of the solids by
  bacteria in the tank.
sequestration (SEE-kwes-TRAY-shun). A chemical
  complexing (forming or joining together) of metallic
  cations (such as iron) with certain inorganic compounds,
  such as phosphate. Sequestration prevents the precipitation
  of the metals (iron). Also see chelation.
service line sample. A one-liter sample of water collected in
  accordance with CFR Section 141.86(b)(3) of the code of
  Federal Regulations, that has been standing for a least 6
  hours in a service  line.
service pipe. The pipeline extending from the water main to
  the building served or to the consumer's system.
set point. The position at which the control or controller is
  set. This is the same as the desired value of the process
sewage. The  used water and solids that flow from homes
  through sewers to a wastewater treatment plant. The
  preferred term is WASTEWATER.
sewage. Liquid and solid wastes carried in sewers.
sewer. An underground system of conduits (pipes and/or
  tunnels) that collect and transport wastewaters and/or
  runoff; gravity sewers carry free-flowing water and wastes;
  pressurized sewers carry pumped wastewaters under
sewerage system. The network of sewers that carries sewage
  from point of origin to point of treatment.
shock load. The arrival at a water treatment plant of raw
  water containing unusual amounts of algae, colloidal
  matter, color, suspended solids, turbidity, or other pollut-
short-circuiting. A condition that occurs in tanks or basins
  when some of the water travels faster than the rest of the
  flowing water. This is usually undesirable since it may
  result in shorter contact, reaction, or settling times in
  comparison with the theoretical (calculated) or presumed
  detention times.
 silt.  Soil particles between 0.05 and 0.002 millimeter in
  approximate diameter.
 simulate. To reproduce the action of some process, usually
  on a smaller scale.
 single family structure. A building constructed as a single-
  family residence that is currently used as either a residence
  or a place of business.
single-stage pump. A pump that has only one impeller. A
  multi-stage pump has more than ne impeller.
sink. A place in the environment where a compound or
  material collects. See reservoir.
slake. To mix with water with a true chemical combination
  (hydrolysis) taking place, such as in the slaking of lime.
slope. The slope or inclination of a trench bottom or a trench
  side wall is the ratio of the vertical distance to the horizon-
  tal distance or "rise over run." Also see grade (2).
slow sand filtration. A process involving passage of raw
  water through a bed of sand at low velocity (generally less
  than 0.4 m/h) resulting in substantial particulate removal by
  physical and biological mechanisms.
sludge (sluj). The settleable solids separated from water
  during processing.
slurry (SLUR-e). A watery mixture or suspension of
  insoluble (not dissolved) matter; a thin watery mud or any
  substance resembling it (such as a grit slurry or a lime
SMCLs. Secondary Maximum Contaminant Levels. Second-
  ary MCLs for various water quality indicators are estab-
  lished to protect public welfare.
SNARL. Suggested No Adverse Response Level. The
  concentration of a chemical in water that is expected not to
  cause an adverse health effect.
soft water. Water having a low concentration of calcium and
  magnesium ions. According to U.S. Geological Survey
  guidelines, soft water is water having a hardness of 60
  milligrams per liter or less.
software programs. Computer programs; the list of instruc-
  tions that tell a computer how to perform a given task or
soil credibility. A measure of the soil's susceptibility to
  raindrop impact, runoff and other erosional processes.
soil profile. A vertical section of the earth's highly weathered
  upper surface often showing several distinct layers, or
soil structure. The arrangement of soil particles  into
soil texture. The proportions of soil particles (sand, silt, and
  clay) in a soil profile.
solder. A metallic compound used to seal the joints between
  pipes. Until recently, most solder contained 50 percent lead.
  The use of lead solder containing more than 0.2% lead is
  now prohibited for pipes carrying potable water.
 sole source aquifer. An aquifer that supplies 50 percent or
  more of the drinking water of an area.
 solenoid (SO-luh-noid). A magnetically (electrical coil)
  operated mechanical device. Solenoids can operate a small
  valve or a switch.
 solution. A liquid mixture of dissolved substances. In a
  solution it is impossible to see all the separate parts.

                                              Drinking Water Glossary
sorption. A surface phenomenon which may be either
  absorption or adsorption, or a combination of the two; often
  used when the specific mechanism is not known.
span. The scale or range of values an instrument is designed
  to measure. Also see range.
specific conductance. A rapid method of estimating the
  dissolved-solids content of a water supply. The measure-
  ment indicates the capacity of a sample of water to carry an
  electrical current, which is related to the concentration of
  ionized substances in the water. Also called conductance.
specific gravity. Weight of a particle, substance, or chemical
  solution in relation to the weight of water. Water has a
  specific gravity of 1.000 at 4 degrees C (39 degrees F).
  Particulates in raw water may have a specific gravity of
  1.005 to 2.5.
specific yield. The quantity of water that a unit volume of
  saturated permeable rock or soil will yield when drained by
  gravity. Specific yield may be expressed as a ratio or as a
  percentage by volume.
spoil. Excavated material such as soil from the trench of a
  water main.
spore. The reproductive body of an organism which is
  capable of giving rise to a new  organism either directly or
  indirectly. A viable (able to live and grow) body regarded
  as the resting stage of an organism. A spore is usually more
  resistant to disinfectants and heat than most organisms.
spring. Ground water seeping out of the earth where the
  water table intersects the ground surface.
spring line. Theoretical center of a pipeline. Also, the
  guideline for laying a course of bricks.
standard. A physical or chemical quantity whose value is
  known exactly, and is used to calibrate or standardize
  instruments. Also see reference.
Standard Methods. See Standard Methods for the Examina-
  tion of Water and Wastewater.
Standard Methods for the Examination of Water and
  Wastewater. A joint ublication of the American Public
  Health  Association, American Water Works Association,
  and the Water Pollution Control Federation which outlines
  the procedures used to analyze the impurities in water and
standard sample. The aliquot of finished drinking water that
  is examined for the presence of coliform bacteria.
standard solution. A solution in  which the exact concentra-
  tion of a chemical or compound is known.
standardize. To compare with a standard. 1) In wet chemis-
  try, to find out the exact strength of a solution by comparing
  it with a standard of known strength. 2) To set up an
  instrument or device to read a standard. This allows you to
  adjust the instrument so that it reads accurately, or enables
  you to apply a correction factor to the readings.
starters. Devices used to start up large motors gradually to
  avoid severe mechanical shock  to a driven machine and to
  prevent disturbance to the electrical lines (causing dimming
  and flickering of lights).
State. The agency of the State or Tribal government which
  has jurisdiction over public water systems. During any
  period when a State or Tribal government does not have
  primary enforcement responsibility pursuant to Section
  1413 of the Safe Drinking Water Act, the term "State"
  means the Regional Administrator, U.S. Environmental
  Protection Agency.
static head. When water is not moving, the vertical distance
  (in feet) from a specific point to the water surface is the
  static head. (The static pressure in psi is the static head in
  feet times 0.433 psi/ft.) Also see dynamic pressure and
  static pressure
static pressure. When water is not moving, the vertical
  distance (in feet) from a specific point to the water surface
  is the static head. The static pressure in psi is the static head
  in feet times 0.433 psi/ft. Also see dynamic pressure and
  static head
static water depth. The vertical distance in feet from the
  centerline of the pump discharge down to the surface level
  of the free pool while no water is being drawn from the
  pool or water table.
static water level. 1) The elevation or level of the water table
  in a well when the pump is not operating. 2) The level or
  elevation to which water would rise in a tube connected to
  an artesian aquifer,  or basin, or conduit under  pressure.
stator. That portion of a machine which contains the station-
  ary (non-moving) parts that surround the moving parts
sterilization (STARE-uh-luh-ZAY-shun). The removal or
  destruction of all microorganisms, including pathogenic and
  other bacteria, vegetative forms and spores. Compare with
stethoscope. An instrument used to magnify sounds and
  convey them to the  ear.
strip cropping. A crop production system that  involves
  planting alternating strips of row crops and close-growing
  forage crops; the forage strips intercept and slow runoff
  from the less protected row crop strips.
stochastic. Based on the assumption that the actions of a
  chemical substance results from probabilistic events.
storm sewer.  A sewer that collects and transports surface
  runoff to a discharge point (infiltration basin, receiving
  stream, treatment plant).
stratification. The formation of separate layers  (of tempera-
  ture, plant, or animal life) in a lake or reservoir. Each layer
  has similar characteristics such as all water in the layer has
  the same temperature. Also see thermal stratification.
subchronic. Of intermediate duration, usually used to
  describe studies or levels of exposure between 5 and 90
submergence. The distance between the water surface and

                                             Drinking Water Glossary
  the media surface in a filter.
submerged aquatic vegetation (SAV). Aquatic vegetation,
  such as sea grasses, that cannot withstand excessive drying
  and therefore live with their leaves at or below the water
  surface. SAVs provide an important habitat for young fish
  and other aquatic organisms.
suction lift. The NEGATIVE pressure [in feet (meters) of
  water or niches (centimeters) of mercury vacuum] on the
  suction side of the pump. The pressure can be measured
  from the centerline of the pump DOWN TO (lift) the
  elevation of the hydraulic grade line on the suction side of
  the pump.
  Chlorination with doses that are deliberately selected to
  produce free or combined residuals so large as to require
Superfund. Federal law which authorizes EPA to manage
  the clean-up of abandoned or uncontrolled hazardous waste
supernatant (sue-per-NAY-tent). Liquid removed from
  settled sludge. Supernatant commonly refers to the liquid
  between the sludge on the bottom and the water surface of a
  basin or container.
supersaturated. An unstable condition of a solution (water)
  in which the solution contains a substance at a concentration
  greater than the saturation concentration for the substance.
supplier of water. Any person who owns or operates a public
  water system.
surface loading. One of the guidelines for the design of
  settling tanks and clarifiers hi treatment plants. Used by
  operators to determine if tanks and clarifiers are hydrauli-
  cally (flow) over- or underloaded. Also called overflow
 surface pump. A mechanism for removing water or waste-
  water from a sump or wet well.
 surface runoff. Precipitation, snow melt, or irrigation in
  excess of what can infiltrate the soil surface and be stored in
  small surface depressions; runoff is a major transporter of
  nonpoint source pollutants.
 surface water. All water naturally open to  the atmosphere
  (rivers, lakes, reservoirs, streams, impoundments, seas,
  estuaries, etc.) and all springs, wells, or other collectors
  which are directly influenced by surface water.
 surfactant (sir-FAC-tent). Abbreviation for surface-active
  agent. The active agent in detergents that possesses a high
  cleaning ability.
 surge chamber. A chamber or tank connected to a pipe and
   located at or near a valve that may quickly open or close or
   a pump that may suddenly start or stop. When the flow of
   water in a pipe starts or stops quickly, the surge chamber
   allows water to flow into or out of the pipe and minimize
   any sudden positive or negative pressure waves or surges in
   the pipe.
suspended solids. l)Solids that either float on the surface or
  are suspended in water or other liquids, and which are
  largely removable by laboratory filtering. 2) The quantity of
  material removed from water hi a laboratory test, as
synergism. An interaction of two or more chemicals which
  results in an effect that is greater than the sum of their
  effects taken independently.
system with a single service connection. A system which
  supplies drinking water to consumers via a single service
systemic. Relating to whole body, rather than its individual
systemic effects. Effects observed at sites distant from the
  entry point of a chemical due to its absorption and distribu-
  tion into the body.
sounding tube. A pipe or tube used for measuring the depths
  of water.
 TCE. See trichloroethane
 TDS. See total dissolved solids.
 telemetry (tel-LEM-uh-tree). The electrical link between
  the transmitter and the receiver. Telephone lines are
  commonly used to serve as the electrical line.
 temperature sensor. A device that opens and closes a switch
  hi response to changes hi the temperature. This device
  might be a metal contact, or a thermocouple that generates
  minute electrical current proportional to the difference hi
  heat, or a variable resistor whose value changes hi response
  to changes hi temperature. Also called a heat sensor
 teratogenesis. The induction of nonhereditary congenital
  malformations (birth defects) hi a developing fetus by
  exogenous factors acting hi the womb; interference with
  normal embryonic development.
 teratogenicity. The capacity of a physical or chemical agent
  to cause teratogenesis hi offspring.
 terrace. A broad channel, bench, or embankment con-
  structed across the slope to intercept runoff and detain or
  channel it to protected outlets, thereby reducing erosion
  from agricultural areas.
 therapeutic index. The ratio of the dose required to produce
  toxic or lethal effect to dose required to produce nonadverse
  or therapeutic response.
 thermal stratification (STRAT-uh-fuh-KAY-shun). The
   formation of layers of different temperatures hi a lake or
  reservoir. Also see stratification
 thermocline (THUR-moe-KLlNE). The middle layer in a
   thermally stratified lake or reservoir. In this layer there is a
   rapid decrease in temperature with depth. Also called the

                                             Drinking Water Glossary
thermocouple. A heat-sensing device made of two conduc-
  tors of diffeent metals joined at their ends. An electric
  current is produced when there is a difference  in tempera-
  ture between the ends.
THM. See trihalomethanes
THM precursor. See precursor, THM.
threshold. The lowest dose of a chemical at which a speci-
  fied measurable effect is observed and below which it is not
threshold odor. The minimum odor of a water sample that
  can just be detected after successive dilutions with odorless
  water. Also called odor threshold
threshold odor number. The greatest dilution of a sample
  with odor-free water that still yields a just-detectable odor.
thrust block. A mass of concrete or similar material appro-
  priately placed around a pipe to prevent movement when
  the pipe is carrying water. Usually placed at bends and
  valve structures.
tillage.  Plowing, seedbed preparation, and cultivation
time lag. The time required for processes and control systems
  to respond to a signal or to reach a desired level.
timer. A device for automatically starting or stopping a
  machine or other device at a given time.
time-weighted  average. The average value of a parameter
  (e.g., concentration of a chemical in air) that varies over
tissue. A group of similar cells.
titrate (TIE-trate). To TITRATE a sample, a chemical
  solution of known strength is added on a drop-by-drop basis
  until a certain color change, precipitate, or pH  change in the
  sample is observed (end point). Titration is the process of
  adding the chemical reagent in increments until completion
  of the reaction, as signaled by the end point.
TNCWS. See transient non-community water system.
too numerous to count. The total number of bacterial
  colonies exceeds 200 on a 47-mm diameter membrane filter
  used for coliform detection.
topography. The arrangement of hills and valleys in a
  geographic area.
total dissolved  phosphorus.  Total phosphorus content of
  material that will pass through a filter of a specific size.
total dissolved  solids (TDS). All of the dissolved solids in a
  water. TDS is measured on a sample of water that has
  passed through a very fine mesh filter to remove suspended
  solids. The water passing through the filter is evaporated
  and the residue represents the dissolved solids. Also see
  specific conductance
total dynamic head (TDH). When a pump is  lifting or
  pumping water, the vertical distance (in feet) from the
  elevation of the energy grade line on the suction side of the
  pump to the elevation of the energy grade line  on the
  discharge side of the pump.
total nitrogen. The sum of all nitrogen forms.
total particulate phosphorus. Total phosphorus content of
  material retained on a filter of a specific size.
total phosphorus. The sum of all phosphorus forms.
total residual chlorine. The amount of available chlorine
  remaining after a given contact time. The sum of the
  combined available residual  chlorine and the free available
  residual chlorine. Also see residual chlorine
total trihalomethanes (TTHMs). The sum of the  concentra-
  tion, in milligrams per liter, of the several trihalomethane
  compounds, rounded to two  significant figures.
total trihalomethanes (TTHM).  The sum of the concentra-
  tion in milligrams per liter of the trihalomethane com-
  pounds (trichloromethane [chloroform],
  dibromochloromethane, bromodichloromethane and
  tribromomethane [bromoform]), rounded to two  significant
totalizer. A device or meter that continuously measures and
  calculates (adds) total flows in gallons, million gallons,
  cubic feet, or some other unit of volume measurement. Also
  called an integrator.
toxaphene (TOX-uh-FEEN).  A chemical that causes
  adverse health effects in domestic water supplies and also is
  toxic to freshwater and marine aquatic life.
toxic (TOX-ick). A substance  which is poisonous to an
toxic pollutants. Materials contaminating the environment
  that cause death, disease, birth defects in organisms that
  ingest or absorb them. The quantities and length of expo-
  sure necessary to cause these effects can vary widely.
toxic substance. A chemical or mixture that may represent an
  unreasonable risk of injury to health or the environment.
toxicant. A harmful substance or  agent that may injure an
  exposed organism.
toxicity. The quality or degree of being poisonous or harmful
  to plant, animal or human life.
toxicityassessment. Characterization of the toxicological
  properties and effects of a chemical, including all aspects of
  its absorption, metabolism, excretion and mechanism of
  action, with special emphasis on establishment of dose-
  response characteristics.
toxicology. The science and study of poisons control.
transducer (trans-DUE-sir). A device which senses some
  varying condition and converts it to an electrical  signal for
  transmission to some other device (a receiver)  for process-
  ing or decision making.
transformation. Acquisition by a cell of the property of
  uncontrolled growth.
TWS. See transient water system.
transient water system. A non-community water system that
  does not serve 25 of the same nonresident persons per day

                                             Drinking Water Glossary
Weir Loading (GPM/ft) = Flow (GPM)/ Length of Weir (ft)   References
well. A bored, drilled, or driven shaft, or a dug hole, whose
  depth is greater than the largest surface dimension and
  whose purpose is to reach underground water supplies or
  oil, or to store or bury fluids below ground.
well field. Area containing one or more wells that produces
  usable amount of water.
well monitoring. The measurement, by on-site instruments or
  laboratory methods, of the quality of water in a well.
well plug. A watertight and gastight seal installed in a bore
  hole or well to prevent movement of fluids.
wet chemistry. Laboratory procedures used to analyze a
  sample of water using liquid chemical solutions (wet)
  instead of, or in addition to, laboratory instruments.
wetlands. Any number of tidal and nontidal areas character-
  ized by saturated or nearly saturated soils most of the year
  that form an interface between terrestrial (land-based) and
  aquatic environments; include freshwater marshes around
  ponds and channels (rivers and streams), brackish and salt
  marshes; other common names include swamps and bogs.
wirc-to-water efficiency. The efficiency of a pump and
  motor together. Also called the overall efficiency.
withdrawal. The process of taking water from a source and
  conveying it to a place for a particular type of use.
Water Treatment Plant Operation. California State Univer-
sity, Sacramento, School of Engineering, Applied Research
and Design Center. 1988.

Surface Water Treatment: The New Rules. Harry von Huben.
American Water Works Association. 1991.

Safe Drinking Water Act Amendments, Regulations and
Standards. Calabrese, EJ; Gilbert, CE and Pastides, H. Eds.
Lewis Publishers. Chelsea Michigan. 1988.

Water Resources Planning. Dzurik, AA. Rowman &
Littlefield, Savage, MD. 1990.

Code of Federal Regulations, Title 40, Chapter I, Section
141.2. July 1, 1991

Federal Register
        56 FR 26547, June 7, 1991 (Lead and Copper)
        56 FR 3578, January 30, 1991 (Phase II)
yield. The quantity of water (expressed as a rate of fiow-
  GPM, GPH, GPD, or total quantity per year) that can be
  collected for a given use from surface or groundwater
  sources. The yiel may vary with the use proposed, with the
  plan of development, and also with economic consider-
  ations. Also see safe yield.
zcta potential. In coagulation and flocculation procedures,
  the difference in the electrical charge between the dense
  layer of ions surrounding the particle and the charge of the
  bulk of the suspended fluid surrounding this particle. The
  zcta potential is usually measured in millivolts.
zone of aeration. The comparatively dry soil or rock located
  between the ground surface and the top of the water table.
zone of saturation. The soil or rock located below the top of
  the groundwater table. By definition, the zone of saturation
  is saturated with water. Also see water table.
zooplankton (ZOE-PLANK-ton). Small, usually micro-
  scopic animals (such as protozoans), found in lakes and