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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
sensed.
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
exposure.
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
substance.
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-
tion).
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
1
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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
minute.
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
solution.
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-
tion.
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)
chlorine.
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).
B
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
solids.
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.
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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
water.
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
reference.
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
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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
ammonia.
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
chemical.
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
SEDIMENTATION BASINS.
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
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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
together.
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
system.
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-
TANCE.
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
influence.
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
operated.
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)
crops.
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
filtration.
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
conditions.
conventional treatment. See conventional filtration Also
called COMPLETE TREATMENT.
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
crops.
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
(monoculture).
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-
ageandbackflow.
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
Regulations.
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.
D
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
AGE TANK.
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
process.
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
8
-------
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
nitrogen.
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
air.
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
ocean.
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
microorganisms.
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
demonstration.
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
organism.
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-
phenylene-diamine.
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.
10
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Drinking Water Glossary
E
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
grams.
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
CERCLA or RCRA.
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
bacteria.
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
11
-------
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
variance.
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
pathogens
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.
12
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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
floods.
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
filter.
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
teeth.
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
EXPANSION
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.
G
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
SERIES.
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.
13
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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.
H
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
iodine.
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
SENSOR.
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.
14
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Drinking Water Glossary
hematopoiesis. The production of blood and blood cells;
hemopoiesis.
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
connected.
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-
sures.
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
rock.
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
15
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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
water.
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-
gation.
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-
ment.
instream uses. Water uses that can be carried out without
removing the water from its source, as in navigation and
recreation.
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
soil.
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.
16
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Drinking Water Glossary
ion. An electrically charged atom, radical (such as S042-), or
molecule formed by the loss or gain of one or more
electrons.
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
agent.
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
motor.
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.
K
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-
charge.
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
metals.
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
line.
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
17
-------
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
instrument.
linearized multistage model. Derivation of the multistage
model, where the data are assumed to be linear at low
doses.
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."
M
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
uranium-238.
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
18
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Drinking Water Glossary
which contain moderate quantities of nutrients and are
moderately productive in terms of aquatic animal and plant
life.
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
(anabolism).
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
THERMOCLINE.
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-
trichloroethane.
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
carbonate.
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
tissues.
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
19
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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
percent.
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
carcinogenicity.
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
recombination.
mutagenicity. The capacity of a chemical or physical agent
to cause permanent alteration of the genetic material within
living cells.
N
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
NIOSH.
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
Regulations.
nitrification. The biochemical transformation of ammonium
nitrogen to nitrate nitrogen.
nitrification inhibitor. A chemical that slows down the
20
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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
compounds.
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
nutrients.
nutrient pollution. Contamination of water resources by
excessive inputs of nutrients; insurface waters, excess algal
production is a major concern.
o
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
ampere.
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
21
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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
bacteria.
organism. Any form of animal or plant life. Also see
bacteria..
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
EFFICIENCY.
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-
taminants.
palatable (PAL-a-ta-ble). Water at a desirable temperature
that is free from objectionable tastes, odors, colors, and
turbidity. Pleasing to the senses.
x
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
22
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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
materials.
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
agency.
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
0.000000000001
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.
23
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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
resource.
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
water.
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
purposes.
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
24
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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.
o
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.
R
radial to impeller. Perpendicular to the impeller shaft.
Material being pumped flows at a right angle to the impel-
ler.
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
rays.
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
indicator.
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
25
-------
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
underground.
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
instruments.
reliquifaction(re-LlCK-we-FACK-shun).
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
tillage.
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
level.
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
26
-------
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-"
chine.
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
consumers.
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
water.
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
facilities.
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
27
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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
variable.
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
pressure.
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-
ants.
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
slurry).
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
tasks.
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
horizons.
soil structure. The arrangement of soil particles into
aggregates.
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.
28
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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
wastewater.
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
(rotor).
sterilization (STARE-uh-luh-ZAY-shun). The removal or
destruction of all microorganisms, including pathogenic and
other bacteria, vegetative forms and spores. Compare with
disinfection.
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
days.
submergence. The distance between the water surface and
29
-------
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.
superchlorination(SUE-per-KLOR-uh-NAY-shun).
Chlorination with doses that are deliberately selected to
produce free or combined residuals so large as to require
dechlorinatin.
Superfund. Federal law which authorizes EPA to manage
the clean-up of abandoned or uncontrolled hazardous waste
sites.
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
rate.
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
prescribed hi STANDARD METHODS FOR THE EX-
AMINATION OF WATER AND WASTEWATER.
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
line.
systemic. Relating to whole body, rather than its individual
parts.
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
METALIMNION.
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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
observed.
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
practices.
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
tune.
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
figures.
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
organism.
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
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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
reservoirs.
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