United States
Environmental Protection
Agency
Office of Water (4601M)
Office of Ground Water and Drinking Water
Distribution System Issue Paper
Potential Contamination Due to
Cross-Connections and Backflow and the
Associated Health Risks
September 27, 2001

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PREPARED BY:
U.S. Environmental Protection Agency
Office of Ground Water and Drinking Water
Standards and Risk Management Division
1200 Pennsylvania Ave., NW
Washington DC 20004
Background and Disclaimer
The USEPA is revising the Total Coliform Rule (TCR) and is considering new possible
distribution system requirements as part of these revisions. As part of this process, the
USEPA is publishing a series of issue papers to present available information on topics
relevant to possible TCR revisions. This paper was developed as part of that effort.
The objectives of the issue papers are to review the available data, information and
research regarding the potential public health risks associated with the distribution
system issues, and where relevant identify areas in which additional research may be
warranted. The issue papers will serve as background material for EPA, expert and
stakeholder discussions. The papers only present available information and do not
represent Agency policy. Some of the papers were prepared by parties outside of EPA;
EPA does not endorse those papers, but is providing them for information and review.
Additional Information
The paper is available at the TCR web site at:
http://www.epa.gov/safewater/disinfection/tcr/regulation revisions.html
Questions or comments regarding this paper may be directed to TCR@epa.gov.

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Potential Contamination Due to
Cross-Connections and Backflow and the
Associated Health Risks
An Issues Paper
by
EPA's Office of Ground Water and
Drinking Water

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1.0 Nature and Purpose of the Paper
This paper is one of nine papers that examine issues related to drinking water distribution
systems. The nine papers are products of two expert workshops. The first workshop, in June 2000,
discussed issues associated with distribution systems that may pose public health risks and identified
those issues of most concern. The distribution system issues of most concern identified at the workshop
are the following: Microbial Growth and Biofilms; Cross-Connections and Backflow; Intrusion;
Corrosion and Aging Infrastructure; Decay of Water Quality over Distribution System Residence Time;
Contamination During Infrastructure Repair and Replacement; Nitrification; Covered Storage; and
Permeation and Leaching. The second workshop, in March 2002, discussed the first drafts prepared on
those issues.
In support of the nine distribution system issue papers, EPA developed two tables that list many
of the biological and chemical contaminants represented in the papers and their potential health effects:
the Microbial Contaminant Health Effects Table (for acute and chronic health effects) and the Chemical
Contaminant Health Effects Table (for chronic health effects). For those contaminants mentioned in this
paper and included in these tables, a reference to the tables is provided for further information on
potential health effects.
The purpose of this document is to review existing literature, research, and information on the
occurrence, magnitude, and nature of the public health risks associated with cross-connections and
backflow, from both acute and chronic exposures, and methods for detecting and controlling the
occurrence of cross-connections and backflow within distribution systems. More specifically, the goal of
this document is to review what we know regarding: (1) causes of contamination through
cross-connections; (2) the magnitude of risk associated with cross-connections and backflow; (3) costs of
backflow contamination incidents; (4) other problems associated with backflow incidents; (5) suitable
measures for preventing and correcting problems caused by cross-connections and backflow, (6) possible
indicators of a backflow incident; and (7) research opportunities.
2.0 Executive Summary
Within distribution systems there exist points called cross-connections where nonpotable water
can be connected to potable sources. These cross-connections can provide a pathway for backflow of
nonpotable water into potable sources. Backflow can occur either because of reduced pressure in the
distribution system (termed backsiphonage) or the presence of increased pressure from a nonpotable
source (termed backpressure). Backsiphonage may be caused by a variety of circumstances, such as main
breaks, flushing, pump failure, or emergency firefighting water drawdown. Backpressure may occur
when heating/cooling, waste disposal, or industrial manufacturing systems are connected to potable
supplies and the pressure in the external system exceeds the pressure in the distribution system. Both
situations act to change the direction of water, which normally flows from the distribution system to the
customer, so that nonpotable and potentially contaminated water from industrial, commercial, or
residential sites flows back into the distribution system through a cross-connection. During incidents of
backflow, these chemical and biological contaminants have caused illness and deaths, with contamination
affecting a number of service connections. The number of incidents actually reported is believed to be a
small percentage of the total number of backflow incidents in the United States.
The risk posed by backflow canbe mitigated through preventive and corrective measures. For
example, preventative measures include the installation of backflow prevention devices and assemblies
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and formal programs to seek out and correct cross-connections within the distribution system and, in
some cases, within individual service connections. Corrective measures include activities such as
flushing and cleaning the distribution system after a detected incident. These may help mitigate any
further adverse health effects from any contaminants that may remain in the distribution system.
3.0 Definition of Key Terms
A cross-connection is a point in a plumbing system where it is possible for a nonpotable
substance to come into contact with the potable drinking water supply (BMI, 1999). According to the
University of Southern California's Foundation for Cross-Connection Control and Hydraulic Research
(USC FCCCHR) (1993), a cross-connection means,
"any unprotected actual or potential connection or structural arrangement between a public or
private potable water system, and any other source or system through which it is possible to
introduce into any part of the potable system any used water, industrial fluids, gas, or substance
other than the intended potable water with which the potable system is supplied."
Common examples of cross-connections include a garden hose submerged in a pesticide mixture, a piped
connection providing potable feed water to an industrial process, such as a cooling tower, or a submerged
outlet of an irrigation system. Connections to firefighting equipment are other very common cross-
connections. Most cross-connections occur beyond the customer service connection, within residential,
commercial, institutional or industrial plumbing systems. Identifying cross-connections can be
challenging because many distribution systems are expanding to serve new customers and changing to
accommodate customer needs. Further, temporary and permanent cross-connections can be created in
existing facilities without the knowledge of the water system managers and operators.
Backflow is any unwanted flow of used or nonpotable water, or other substances from any
domestic, industrial, or institutional piping system back into the potable water distribution system1 (USC
FCCCHR, 1993). The direction of flow under these conditions is opposite to that of normal flow. The
reverse pressure gradient that leads to backflow is caused by either backsiphonage or backpressure (USC
FCCCHR, 1993; BMI, 1996).
Backsiphonage is backflow caused by negative or sub-atmospheric pressure in a portion of the
distribution system or the supply piping (USC FCCCHR, 1993). When the system pressure drops to
below atmospheric (negative gauge pressure), ambient pressure on the distribution system due to the
atmosphere, water columns (frombuildings or other elevated piping), or other sources will cause the
direction of flow within portions of the system to reverse. If a cross-connection exists in the area where
flow reverses direction, contaminants can be siphoned into the distribution system (USC FCCCHR,
1993). Water main breaks, firefighting efforts, high demands, and any situation where water is
withdrawn from the distribution system at a high rate can lead to backsiphonage (USC FCCCHR, 1993).
Backpressure can cause backflow to occur when a potable system is connected to a nonpotable
supply operating under a higher pressure than the distribution system by means of a pump, boiler,
elevation difference, air or steam pressure, or other means (USC FCCCHR, 1993). Unlike
'This paper defines the distribution system to be from the point at which the water leaves the treatment
plant, or source, if untreated, to the point at which the customer's service line begins.
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backsiphonage, it is not necessary to have a drop in distribution system pressure for backpressure to
occur. Whenever the pressure at the point of a cross-connection exceeds the pressure of the distribution
system, the direction of flow will reverse. There is a high risk that nonpotable water will be forced into
the potable system whenever these connections are not properly protected (USC FCCCHR, 1993).
4.0	What Causes Contamination Through Cross-Connections to Occur?
This section of the paper describes how cross-connections and backflow occur, and what
conditions and situations are necessary to cause them. Under intended flow conditions, distribution
systems are pressurized to deliver finished water from the treatment plant to the customer. However, two
situations can cause the direction of flow to reverse: pressure in the distribution system can drop due to
various conditions or an external system connected to the distribution system may operate at a higher
pressure than the distribution system. These differences in pressure can cause contaminants to be drawn
or forced into the distribution system. Contamination introduced due to backflow into the distribution
system may then flow freely into other customer connections. The following conditions must be present
for contamination to occur through cross-connections.
•	A cross-connection exists between the potable water distribution system and a nonpotable
source.
•	The pressure in the distribution system either becomes negative (backsiphonage), or the
pressure of a contaminated source exceeds the pressure inside the system (backpressure).
•	The cross-connection is not protected, or the connection is protected and the mechanism
failed, allowing the backflow incident.
The extent of contamination in the distribution system depends, in part, on the location of the
cross-connection, the concentration of the contaminant entering the distribution system and the
magnitude and duration of the pressure difference causing the backflow. This section of the paper
describes the theory of backflow and cross-connections, provides examples of conditions that can create
backflow, and lists a number of factors that affect the likelihood and magnitude of backflow through a
cross-connection.
4.1	Backflow Conditions
The occurrence of backflow is directly related to system pressure. Any pressure differential
between the potable water and the non-potable source can lead to backflow. It is estimated that even
well-run water distribution systems experience about 25-30 breaks per 100 miles of piping per year (Deb
et al., 1995). Haas (1999) reported results from a survey of water systems that showed a range of average
main breaks of 488 per year for systems serving more than 500,000 people, to 1.33 per year for systems
serving fewer than 500 people.
Fighting fires also reduces a system's pressure (AWWA, 1999). For example, in 1974 in
Washington State, the high rate of flow caused by the activation of a fire deluge system reduced pressure
in a domestic water line, causing backsiphonage of a chemical and other pollutants into the potable water
system (AWWA PNWS, 1995). Similarly, opening hydrants during the summer for recreational use
causes pressure to drop. Regular system maintenance activities such as valve exercising programs,
hydrant flushing, pump repair, pressure control valve repair, and valve replacement can also result in
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localized variations in pressure that cause backflow. Differences in elevation can compound the effects
of pressure loss.
Additionally, if a high pressure source is connected to the distribution system, a drop in pressure
is not necessary for backflow to occur—the presence of a cross-connection or failure of the prevention
mechanism will allow backflow to occur.
Examples of backsiphonage
Elevated piping can cause backsiphonage when there is a loss of pressure in the supply system.
The loss of pressure will cause the water column to collapse and create a vacuum that can draw
contaminants in through a cross-connection (BMI, 1999; USC FCCCHR, 1993). Backsiphonage can also
occur within irrigation systems. For example, in 1991, a water main break lead to the backsiphonage of
parasitic worms from a residential lawn sprinkler supply into two homes (AWWA PNWS, 1995).
Booster pumps for high-rise buildings can cause backsiphonage if the suction lines of the pumps
are being used for service on the lower floors and a temporary or permanent cross-connection on the
lower floors exists (e.g., a hose submerged in a bucket of cleaning solution). If distribution system
pressure drops, the suction pressure can cause the backsiphonage through the lower floor cross-
connection when the pump is operating, contaminating the higher floors (BMI, 1999; USC FCCCHR,
1993; US EPA, 1989).
Localized physical restrictions in water lines can produce backsiphonage through the venturi
effect (BMI, 1999). When water flows through a restriction—for example, through a garden hose or
from a larger water line into a smaller one—its velocity increases and its pressure decreases
proportionately (US EPA, 1989). This decrease in pressure can yield negative pressure and siphon
substances into the point of restriction (BMI, 1999). Devices such as chemical sprayers used on the end
of garden hoses use this principle to siphon chemical from the container into the water stream (BMI,
1996).
Backsiphonage can occur when supply piping within an industrial facility is elevated over the
rim of a vessel, and the outlet of that piping is submerged in a liquid contaminant. Negative distribution
system pressure would cause the water column in the elevated pipe section to collapse, creating a vacuum
that draws contaminants from the vessel into the distribution system (BMI, 1999; USC FCCCHR, 1993).
If a pipe with cracks or leaking joints is exposed to a wet environment, negative pressure can
cause water to be drawn in (or to intrude into) the distribution system through backsiphonage (Kirmeyer
et al., 2001). A separate issue paper addresses risks from intrusion due to pressure transients.
Examples of backpressure
Backpressure can occur with pressurized residential, industrial, institutional, or commercial
systems which use pumps, including chemical feed pumps or booster pumps, or pressurized auxiliary
water systems for irrigation, fire protection, car washes, and cooling systems (USC FCCCHR, 1993;
FDEP, 2001). For example, backpressure resulting from tank cleaning activities by a gas company in
Connecticut caused propane to backflow into the distribution system, causing fires in two homes and
evacuation of hundreds of people. Gas company workers were purging a propane tank with water and
did not realize the pressure in the tank was greater than in the water line feeding the tank, thus creating a
backpressure of propane vapor into the distribution system (US EPA, 1989). Backpressure also occurred
in 1991 at a facility that transforms wheat and barley into ethanol in Tucumcari, New Mexico. An
unprotected auxiliary water line feeding emergency fire cannons was illegally tapped to a hose connected
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to an ethanol plant's flushing system, creating a cross-connection. After the plant finished its flushing
operation, the plant resumed normal operations with the hose still connected, and backpressure from
plant operations forced a number of industrial chemicals to backflowinto the public water supply
(toluene, phenol, benzene, ethanol, nonanoic acid, decanoic acid, octanol, octanoic acid, heptanoic acid,
butanoic acid, silicon, diconic acid and four trihalomethanes). The concentrations of these toxins were
enough to cause the mayor of the town to become very ill for 48 hours. Another individual drank a small
amount of water and became ill with stomach upset. Fortunately, there were no deaths, and the
distribution system was thoroughly flushed after the contamination was detected (AWWA PNWS, 1995).
The likelihood of backpressure increases when the distribution system pressure drops to below normal
operating pressure due to changes in valve setting, pipeline breaks, air valve slams, loose-fitting service
meter connections, surge or feed tank draining, or a sudden change in demand (Kirmeyer et al., 2001).
The weight of water in piping of high-rise buildings is a source of backpressure on the
distribution system. Backpressure can also come from thermal expansion (high pressures can be
generated when water is heated in a closed container). Thermal expansion can occur in boilers, solar
heating systems, and places where water- or foam-based fire sprinkler systems are located on the highest
floors of tall buildings and temperatures of piping rise (BMI, 1999).
Compressed air systems such as carbonators can pose backpressure risks. The pressure of a
carbon dioxide tank, for example, can be several thousand pounds per square inch (psi). This high-
pressure carbon dioxide is passed through a regulator and mixed into a water system at anywhere from
60 to 150 psi. Carbon dioxide from either a tank or a regulator could be introduced to the distribution
system pressure if a cross-connection is present and the compressed air system overcomes the
distribution system pressure (Guy, 1997).
4.2 Factors Affecting the Occurrence and Magnitude of Backflow Contamination
Operating pressure
A minimum operating pressure of 20 psi at all locations in a distribution system is suggested by
various manuals and codes of good operating practice (Kirmeyer et al., 2001). Some states also have
minimum operating pressure requirements. Local operating pressure in a system varies among zones. In
a highly pressurized system, a great deal of backpressure would be needed to force water to backflow; a
system or part of a system with relatively low pressure would generally be more susceptible to
backpressure. Systems with normal operating pressure lower than recommended by manuals and codes
of good practice may have a higher risk of backpressure events.
Reduced pressures that can lead to backflow occur from a variety of sources. Water main breaks,
hilly terrain, limited pumping capacity, high demand by consumers, fire fighting flows, rapidly opening
or closing a wive within the distribution system, power loss, and hydrant flushing can reduce pressure
and contribute to lower or extremely fluctuating water pressures (Kirmeyer et al., 2001). A study of a
distribution system (LeChevallier et al., 2001) observed that during a pump test, routine operation, and a
power outage, pressures as low was -10.1 psi were recorded, with durations ranging from 16 to 51
seconds. During these times of negative pressure, the chance that water external to the distribution
system intruded into the distribution system due to backsiphonage or backpressure increased. In a simple
single pipe model employed in the study, a surge generated by a simulated power failure to a pump
predicted 69 gallons of external water would intrude into the pipe within 60 seconds. A surge caused by a
main break predicted 78 gallons of water intruding within 60 seconds. A survey of 70 systems reported
11,186 pressure reduction incidents in the past year; 34.8 percent of the incidents were from routine
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flushing, 19.2 percent were due to main breaks, and 16.2 percent incidents were due to service line
breaks (ABPA, 2000). Hills and other elevations compound pressure loss effects caused by main breaks,
fire flows, and other events (ABPA, 2000). Limited pumping capacity may cause periodic termination of
water supply in areas of the system. Without sufficient redundancy in the distribution system,
backsiphonage conditions may occur if one or more major components of the distribution system go
offline or otherwise cease functioning.
Physical security of the distribution system
Homeland security initiatives include attention to the physical security of water distribution
systems. The subject of homeland security is well beyond the scope of this paper, but it is relevant to
note that the potential for intentional contamination of a distribution system through cross-connections
and backflow of chemical and biological contaminants is possible (Dreazen, 2001).
Maintenance activities
Maintenance levels and practices within the distribution system can affect the likelihood of
occurrence of cross-connections and backflow. In a South Carolina system in 1978 fifteen people
became ill due to backsiphonage of chlordane from an exterminator truck during meter repair (USC
FCCCHR, 1993). In May, 1982 maintenance crews in Bancroft, Michigan shut down a main to replace a
valve. The resultant pressure loss caused backflow of malathion from a hose end applicator , and
resulted in the loss of water to the village for two days (USC FCCCHR, 1993). The herbicide Lexon DF
backsiphoned into the distribution system in Gridley, Kansas in 1987 from a tanker truck when a main
broke during excavation and contaminated ten residences and one business (USC FCCCHR, 1993).
Levels of public awareness
A lack of public awareness about the threat posed by cross-connections and backflow can lead to
unintentional creation of cross-connections, such as through illegal and unprotected taps into the
distribution system. In 1979, a professional exterminator left a garden hose submerged in a barrel of
diluted pesticide, allowing chlordane to be backsiphoned into the distribution system during a service
interruption (US EPA, 1989). This potential is magnified in multi-storied buildings that have many
people living under one primary connection. Cross-connections are often installed by the public as a
matter of convenience without regard to possible dangers, and others with reliance on inadequate
backflow prevention (US EPA, 1989).
5.0	The Magnitude of Risk Associated with Cross-Connections and Backflow
This section describes the risk posed by contaminants that can enter the distribution system
through cross-connections. The history of outbreaks and reported illnesses associated with cross-
connections and backflow indicates some level of public health risk is associated with cross-connections
and backflow. Risk is a function of a variety of factors including cross-connection and backflow
occurrence, type and amount of contaminants, and their potential health effects. This section first
describes the reported outbreaks of disease associated with cross-connections and backflow, then follows
with a description of some contaminants that have been introduced to distribution systems via cross-
connections and backflow, and the difficulties in detecting and reporting backflow incidents.
5.1	Reported Outbreaks Associated with Cross-Connections and Backflow
From 1981 to 1998, CDC documented 57 waterborne disease outbreaks related to cross-
connections, resulting in 9,734 illnesses. These include 20 outbreaks (6,333 cases of illness) caused by
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microbiological contamination, 15 outbreaks (679 cases of illness) caused by chemical contamination,
and 22 outbreaks (2,722 cases of illness) where the contaminant was not reported. Craun and Calderon
(2001) report that 30.3 percent of waterborne disease outbreaks in community water systems during
1971-1998 were caused by contamination of water in the distribution systems. Of these waterborne
disease outbreaks caused by distribution system deficiencies, 50.6 percent were due to cross-connection
and backflow (Craun and Calderon, 2001). Documented acute health impacts most often involve
gastrointestinal disorders. The data from the CDC's surveillance of the outbreak of waterborne disease
must meet certain documentation standards; therefore, these reports are reliable. However, CDC's
reporting standards exclude some incidents that lack complete documentation and report only outbreaks
of notifiable diseases (a set of diseases that CDC tracks; these do not include endemic diseases). As a
result, these data are likely under-estimates and these under-est.imat.es are compounded by the number of
illnesses that go unreported. (Section 5.4 further discusses the difficulties of detecting and reporting
waterborne disease outbreaks.)
Estimates of the proportion of waterborne illness attributable to cross-connections and backflow
vary. A compilation by EPA's Health Effects Research Laboratory found that between 1920 and 1980,
cross-connections and backflow caused 78 percent of outbreaks, and 95 percent of the cases of illness,
attributed to community distribution system contamination in the United States (A WW A, 1990).
Data on health impacts are also available from other sources that collect information on
backflow incidents, such asUSC FCCCHR, and the Cross-Connection Control Committee of the Pacific
Northwest Section of the AWWA. These independent organizations do not limit their data to well-
defined outbreaks, but focus on incidents. Because not all incident reports document illness, estimates of
illness resulting from an individual incident based on their data are less reliable than CDC estimates of
reported outbreaks.
Our compilation of backflow incident data (summarized in Exhibit 5.1) found that 459 incidents
resulted in an estimated 12,0932 illnesses from 1970 to 2001. When we narrowed the analysis to 1981-
1999, for comparison with CDC data on outbreaks for that period, we found that only 97 of 309 incidents
produced reports of how many (if any) illnesses were caused, and 22 of these 97 incidents reported no
illnesses. Of the remaining 75 incidents, only 26 appear in CDC's summaries as a waterborne disease
outbreak. This suggests that CDC data underreport even known instances of illness caused by backflow
contamination. From the 75 incidents that produced reports of illness, analysis of the qualitative and
quantitative case reports estimated 4,416 illnesses, averaging 46 illnesses per outbreak.
5.2 Contaminants Associated with Cross-Connections and Backflow and Their Health
Effects
A variety of contaminants have been introduced into distribution systems by cross-connections
and backflow, indicated by the backflow occurrence discussed in this paper. The likelihood and severity
of illness and number of people affected depend on various factors including how much contamination
2
If the number of illnesses was reported qualitatively, the analysis used the following assumptions to
estimate a total figure. Specifically, if the number of illnesses was reported as "several", "many", or "numerous", the
analysis assumed five. The analysis assumed that "some" meant three. One incident reported "dozens" of
illnesses this analysis assumed 36. Another rep orted one family the analysis assumed three people.
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enters the system, the dilution factor, the type of contaminant, the number of users exposed, and the
health status of each person at the time of exposure.
Contamination from cross-connections and backflow can occur not only where the cross-
connection is located but at sites upstream and downstream, as contaminants spread. The fate and
transport of a contaminant are often system-specific and can be difficult to predict because they depend
on multiple parameters such as the hydraulics of the distribution system and the physical, chemical, or
biological properties of the contaminant. The contaminant may remain as a slug, resulting in very high
concentrations in localized areas, or it may disperse, contaminating large volumes of water at lower
concentrations. It may adsorb to the interior of pipes, necessitating their cleaning or replacement. It may
degrade, or in the case of microorganisms, be inactivated or injured by residual disinfectant. It may also
become concentrated within the biofilms and be slowly released through erosion or as a slug through
biofilm sloughing. Scales within the piping may adsorb the contaminants for later release.
The Chemical and Microbial Health Effects Tables, developed by EPA to support the nine issue
papers, include many biological and chemical contaminants mentioned in the papers. However,
additional contaminants not listed in these tables are described in this paper because the types of
contaminants that have entered distribution systems through cross-connections are numerous and not
discussed in any other white papers; thus more appropriately described in this paper. For those
contaminants listed in the Health Effects Tables, this paper references the appropriate table for more
information on potential health effects.
5.2.1 Chemical Contaminants
The use of chemicals at residential, industrial, and commercial facilities with direct or indirect
connections to potable water systems presents an opportunity for contamination from cross-connections
and backflow (USC FCCCHR, 1993). Many of these chemicals have some degree of toxicity, and
exposure to these chemicals can have either acute or long-term health effects, depending on the nature
and concentration of the contaminant, duration of exposure, and a person's immune status. Exposure
from contamination through a cross-connection can be either acute or chronic. While waterborne
outbreaks are under-reported in general, rarely are waterborne chemical outbreaks reported to CDC. The
reasons for under-reporting of chemical outbreaks above and beyond that of microbial outbreaks include:
1) most poisonings of this nature (e.g., lead and copper from plumbing) probably occur in private
residences, affect relatively few people and, thus, may not come to the attention of public health
officials; 2) exposure to chemicals via drinking water may cause illness that is difficult to attribute to
chemical intoxication, or it may cause non-specific symptoms that are difficult to link to a specific agent;
and 3) the chemical outbreak detection mechanisms, as well as the reporting requirements are not as well
established as they are for microbial agents (CDC, 1996). Most reported incidents are acute exposures,
however, chronic exposures are possible if immediate water quality or health effects are not noticed, or if
cross-connections remain uncorrected long-term. This can result in some of the chronic health effects
described in the Chemical Health Effects Table (US EPA, 2002a), when the consumer is exposed to the
chemicals listed for a long period of time. Depending on the contaminant, these chronic exposures can
cause long-term health effects, including cancer, which may not be identified until many years after the
initial exposure. Acute health risks include vomiting, bums, poisoning, and other reactions—some
potentially life-threatening. For example, in Rochester, NY, a faulty carbonation system on a soft drink
machine continuously leaked carbon dioxide into the distribution system for over 3 months, creating
increased levels of copper in the distribution system (as high as 13,400 ppb) (Manioci, 1984).
Contamination at the K-25 atomic bomb plant in Oak Ridge, TN, occurred for an unknown length of
time (possibly on the order of decades) through cross-connections with cooling system and firefighting
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lines. Contaminants found at the source of contamination that may have entered the distribution system
included strontium-90, arsenic, chromium, and antifreeze (Nashville Tennessean, 2000).
Because few backflow incidents are reported, it is important to note that a variety of chemicals
have the potential to enter the distribution system through cross-connections, and the number of those
reported only represent a subset. For example, agricultural applications contain many fertilizers,
herbicides, and insecticides and industrial sources such as cooling systems, plating plants, steam boiler
plants, and dye plants have a number of toxic chemicals in day-to-day use that have the potential to
contaminate the distribution system (USC FCCCHR, 1993). The most common chemical contaminants
reported, according to information EPA has obtained from backflow incident records, are (in order of
decreasing occurrence): copper, chromium, ethylene glycol, detergents, chlordane, malathion, propylene
glycol, freon, and nitrite. Chlordane and malathion are pesticides; ethylene glycol is used as antifreeze in
heating and cooling systems, propylene glycol is used as antifreeze and as a food additive; detergents are
extensively used in many industries; copper is used in plumbing; chromium VI was used in the past in
cooling towers as a rust and corrosion inhibitor; and nitrite is a reduced form of nitrate, an agricultural
fertilizer. This summary discusses these and other related chemical contaminants (grouped into four
categories—pesticides, metals, synthetic organic compounds, and nitrates and nitrites) in terms of
potential health effects and examples of reported backflow incidents.
Pesticides
Pesticides (including insecticides, herbicides, and fungicides) as a group are contaminants in 45
reported incidents. Chlordane, malathion, heptachlor, and diazinon were reported as contaminants in 11,
5, 3, and 2 incidents, respectively. In one 1976 incident in Chattanooga, TN, chlordane was being used
for termite extermination and contaminated a three-block area of residential homes; 17 people reported
they drank the suspect water. Reported symptoms by those people were nausea, abdominal pain,
gastrointestinal problems, and neurological effects such as dizziness, blurred vision, irritability,
headache, paresthesia, muscle weakness, and twitching (AWWA PNWS, 1995). In 1980, heptachlor and
chlordane contaminated a portion of distribution system in Allegheny, PA that serviced approximately
300 people. A pesticide contractor created the cross-connection with a garden hose submerged in the
chemical mixing tank. There were no reports of illness, however, residents were without water for 27
days (Watts, 1998). Another pesticide incident involved diazinon contamination in Tucson, AZ in 1989.
Diazinon entered the system through a residential connection where a home-made pesticide pump system
was hooked up to a garden hose. The combination of backpressure from the pump system and the water
use by a next-door neighbor washing a car caused the pesticide to flow into the distribution system
(Tucson Citizen, 1989). No illnesses were reported. In 1986, two employees of a Kansas grain mill
became ill after drinking water contaminated with malathion that was backsiphoned into the plant's
water supply (AWWA PNWS, 1995). In 1988, a Florida man died of insecticide intoxication after he
stepped off his mower, filled his water bottle, and drank from the bottle that was filled with contaminated
water from a faucet at an airstrip. Officials suspected backflow as the cause of the water supply
contamination (AWWA PNWS, 1995).
An example of a small amount of contamination resulting in a public health threat is a 1991
incident where 2.5 gallons of the herbicide TriMec backsiphoned into the Uintah Highlands water system
in Utah affecting 2,000 homes (US EPA, 1989). Shortly thereafter, concentrations of the active
ingredients, 2,4-D and Dicamba, at a consumer's tap were measured at 638 and 64.8 parts per million
(ppm), respectively. This incident also affected a nursing home and a day-care facility, both of which
serve higher risk subpopulations. The health advisory level of both 2,4-D and Dicamba over a 10-day
period is 0.3 ppm (US EPA, 2000a). Chronic health effects of 2,4-D and Dicamba include damage to the
nervous system, kidney, and liver (US EPA, 2002a). However, only acute exposures were documented.
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Metals
There are 73 reported backflow incidents with metal contaminants—55 with copper and 18 with
hexavalent chromium. Copper contamination is most commonly associated with backflow incidents at
restaurants, where carbonated water can dissolve portions of water or soft drink dispenser piping made of
copper. In 1987, a child in Minnesota suffered acute copper toxicity when the backflow from a carbon
dioxide machine contaminated a restaurant's potable system (AWWAPNWS, 1995). A similar incident
at a fair in Springfield, MO, caused vomiting and abdominal pain in three people who drank soft drinks
from a soft drink machine that had a faulty check valve (AWWAPNWS, 1995). Potential health effects
due to copper poisoning include vomiting, nausea, and liver and kidney damage; refer to the Chemical
Health Effects Table for other potential health effects (US EPA, 2002a). CDC reports that the observed
acute health effects due to copper poisoning outbreaks are gastrointestinal illness (CDC, 1996).
Chromium is used as a corrosion inhibitor. In 1970, a cross-connection between a chromate-
treated cooling system and the water supply at Skidmore College in New York, New York, caused five
people to become nauseated (USC FCCCHR, 1993). In another incident in New Jersey in 1970,
hexavalent chromium contamination occurred through a cross-connection of a building heating system
and soft drink machine causing 11 people to become nauseated (USC FCCCHR, 1993). Potential
chronic health effects are listed in the Chemical Health Effects Table (US EPA, 2002a).
Synthetic and volatile organic compounds
Synthetic and volatile organic compounds as a group are contaminants in 66 reported incidents,
with the most frequent contaminants being ethylene glycol (used in antifreeze), propylene glycol (used in
antifreeze and as a food additive), freon (refrigerant), and propane (fuel).
Ethylene and propylene glycol were contaminants in 16 and 5 reported incidents, respectively.
Examples include one incident in 1982, when ethylene glycol backsiphoned from an air conditioning
system's water holding tank into a group of dialysis machines contributing to the death of "several"
patients in Illinois (AWWA PNWS, 1995). In 1985, backpressure from a hospital air conditioning
system caused the introduction of ethylene glycol into the water system of a New York hospital. One
woman died after being exposed while undergoing dialysis (CDC, 1987). In 1987, a cross-connection
with a heating system contaminated the plumbing at a municipal building in North Dakota with ethylene
glycol, causing acute illness in 29 people. Water from a spigot used to make flavored drinks contained 9
percent ethylene glycol. Reported health effects included excessive fatigue and dizziness, while two
children experienced vomiting, excessive fatigue, and hematuria (CDC, 1987). Backflow of propylene
glycol from a fire suppression system in 1993 into the potable water system of a park in Arizona
occurred for at least 2 months before the point of entry was identified. Several employees reported
nausea and intestinal upsets after drinking water during the period of contamination (Watts, 1998), which
was discovered by taste and odor complaints.
Freon and propane were contaminants in four and three reported incidents, respectively. In
1989, backpressure from a propane tank car forced propane into the water supply of Fordyce, Arkansas.
Three people in separate buildings were injured from explosions after flushing toilets, and two houses
were destroyed and a business was damaged by explosions and subsequent fires (AWWA PNWS, 1995).
Backpressure from an air conditioning unit caused freon to backflow into the distribution system in
Franklin, NE. The contamination was detected when city residents complained of bad tasting water that
caused a burning sensation in the mouth (AWWAPNWS, 1995).
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Detergents were contaminants in nine reported incidents. Contamination of concentrated soap in
1995 from an incorrectly installed soap dispenser at a health care facility in Iowa affected 13 people was
reported a burning sensation in their mouths and symptoms resembling the flu (CDC, 1998). In 1993 in
Seattle, WA a temporary cross-connection at a car wash facility allowed soapy water in the distribution
system, affecting an eight block area and causing two unconfirmed cases of illness (AWWA PNWS,
1992).
Nitrates and nitrites
Nitrates and nitrites were contaminants in four reported incidents. Nitrate is a common ion
found in natural waters and is used in fertilizers. Nitrite is typically not observed at significant levels
(AWWA, 2001), however nitrate reduces to nitrite in the human body. In one incident in the county
courthouse building of Monterey, CA, sodium nitrate from the boiler and cooler system backflowed into
the potable water supply through a faulty backflow prevention device. Nineteen people became sick and
needed medical attention from drinking coffee from the courthouse snack bar (AWWA PNWS, 1995).
An incident of nitrite contamination at a school in California caused illness in three people; a faulty
double-check valve allowed chemicals from the chilling system to enter the school's potable water
system (CDC, 1998). Another backflow incident through a cross-connection with a boiler and a faulty
backflow prevention device occurred in New Jersey, causing six people to become ill with
methemoglobinemia caused by nitrites (CDC, 1998). Potential health effects of nitrate consumption
include diuresis and hemorrhaging of the spleen, among others (US EPA, 2002a).
5.2.2 Biological Contaminants
The risks posed by backflow of biological contaminants vary dramatically depending on the
disease vector, the concentration and degree of infectivity of the pathogen, the level of disinfectant
residual maintained by the water system, and the health of the individual exposed (Rusin et al., 1997).
Infective dose studies of non-primary (opportunistic) pathogens on healthy individuals and animals, using
the oral and intranasal route, demonstrate that very high doses (e.g., for bacteria, 106 -1010 cells) are
needed for infection or disease (Rusin et al., 1997).
Pathogenic microorganisms (e.g., Giardia, some strains of is. colt) have contaminated potable
water supplies through cross-connections with sewer lines, untreated surface water sources, reclaimed
water supplies, equipment at medical facilities and mortuaries, and utility sinks, pools, and similar
receptacles. In addition, drain lines, laboratories, and illegal connections of private wells and cisterns to
public water supplies are primary sources of contamination (USC FCCCHR, 1993).
A majority of microbial incident reports (32 of 58) list the microbial contaminant as "sewage" or
nonspecific microbes. In the summer of 1990, 1,100 guests of a country club in Tennessee suffered
intestinal disorders in two mass incidents after consuming the club's contaminated water supplied from
an auxiliary well that had become contaminated with sewage due to a cross-connection (AWWA PNWS,
1995). In February, 1990, a cross-connection between an auxiliary irrigation system supporting a golf
course and country club and the Seattle Water Department's distribution system resulted in total and
fecal coliform contamination that was detected by neighboring systems purchasing water (AWWA
PNWS, 1995). The health effects from pathogens are often not specifically reported in the incident
reports, making it more difficult to determine the type of microbial contaminant. The combination of
these reporting issues leads to underreporting of contamination linked to a specific pathogen.
The general health effects of most microbial pathogens include fever, nausea, and diarrhea, while
some diseases have long-term and/or life-threatening effects. For example, the protozoan Giardia (a
contaminant in 12 reported incidents) causes severe and potentially long-term diarrhea, accompanied by
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excessive gas, bloating, and weight loss. The Microbial Health Effects Table lists these general health
effects and other potential diseases (US EPA, 2002b); however, the table is not all inclusive; additional
potential health effects exist.
From backflow incident records collected by EPA, the most common microbial contaminants
and their potential health effects are listed below with examples of backflow incidents.
Shigella
Shigella species are a cause of gastroenteritis, and are reported as contaminants in five incidents.
The associated symptoms are vomiting, diarrhea, fever, and convulsions (US EPA, 2002b). All species
of Shigella are highly infectious in humans and are spread through ingestion of fecal contamination (US
FDA, 2001a). In one incident in 1977, a cross-connection led to four cases of shigellosis in an apartment
house in Chicago, Illinois (USC FCCCHR, 1993). It is unknown whether the cross-connection spread
Shigella into the distribution system.
E. coli
E. coli, a common biological contaminant (reported as a contaminant in two incidents) that is
found in sewage, is normally a benign intestinal bacterium that is present in every human. However,
some strains of E. coli are pathogenic, and can cause a variety of internal disorders. The most common
effect is watery diarrhea, with some strains causing fever or dysentery. In rarer cases, some strains of
E. coli can cause persistent diarrhea in young children, and have hemolytic properties. An infamous
strain ofis. coli is strain 0157:H7, which, in addition to causing bloody diarrhea, can cause kidney
failure (US EPA, 2002b). In 2000, two outbreaks of is. coli occurred in Medina County, OH, where
approximately 30 became ill (Cleveland Plain Dealer, 2001).
Salmonella
Salmonella is one of the primary intestinal bacterial waterborne pathogens (reported as a
contaminant in one incident). Depending on the strain, health effects can include typhoid fever,
gastroenteritis (salmonellosis) (Benenson, 1995), and septicemia (US EPA, 2002b). In one incident, 750
people became ill with Salmonella enteritidis in Richland, Washington, in 1983. The incident involved
new plumbing and contaminated ice (CDC, 1984). A person infected with the Salmonella enteritidis
bacterium usually has fever, abdominal cramps, and diarrhea beginning 12 to 72 hours after consuming a
contaminated food or beverage. The diarrhea can be severe, and the person may be ill enough to require
hospitalization (CDC DBMD,2001).
Campylobacter jejuni
Campylobacter jejuni is an avian gut bacteria that is the primary cause of bacterial diarrhea in
the United States (CDC, 2002b). It is estimated that Campylobacter infects over two million people a
year, and 10,000 cases are reported to the CDC annually, despite limited monitoring. Although
Campylobacter is primarily a foodborne pathogen, it has been implicated in waterborne disease
outbreaks in the past (CDC, 1996). This bacteria can cause gastroenteritis with symptoms including
bloody diarrhea, fever, and abdominal cramping (US EPA, 2002b). In extreme cases, a Campylobacter
infection may lead to Guillain-Barre syndrome where the immune system attacks part of the nervous
system (CDC, 2002b). In 1986, 250 people became ill with diarrhea due to Campylobacter
contamination in Noble, OK (CDC, 1996).
Cyanobacteria
Cyanobacteria are photo synthetic free-living bacteria. They produce algal blooms in fresh water,
which can result in elevated toxin levels. Cyanobacterial toxins can produce acute neurotoxicity,
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hepatotoxicity, gastroenteritis, respiratory ailments, skin irritation, and allergic reactions through contact
or ingestion (CDC, 2002c). In one incident in 1992, in Ritzville, Washington, backsiphonage from a
drain sump near a new reservoir caused a reoccurring contamination of cyanobacteria (AWWA PNWS,
1995).
Norwalk and Norwalk-like viruses
The Norwalk family of viruses is a cause of viral gastroenteritis with symptoms of vomiting,
diarrhea, upper respiratory problems, and fever (US EPA, 2002b). Although viral gastroenteritis is
caused by a number of viruses, it is estimated that Norwalk or Norwalk-like viruses are responsible for
about 1/3 of the cases of viral gastroenteritis not involving the 6-to-24-month age group (US FDA,
2001b). People often develop immunity to the Norwalk virus, however, it is not permanent and
reinfection can occur (US FDA, 2001b). In developing countries the percentage of individuals who have
developed immunity is very high at an early age. In the United States, the percentage increases gradually
with age, reaching 50 percent in the part of the population over 18 years of age. Norwalk or Norwalk-
like viruses were reported as a contaminant in two incidents. In one incident in 1980 in Lindale,
Georgia, 1,500 people became ill with a Norwalk-like acute gastrointestinal illness as a result of a
contamination incident for which the specific chemical or microbiological contaminant was never
determined (CDC, 1982).
Giardia
Giardia was a contaminant in 12 reported incidents. Giardia are intestinal parasites that exist in
natural waters in a nonreproductive stage (cysts). They can cause diarrhea, as well as vomiting, cramps,
and bloating (US EPA, 2002b). The mode of infection is through ingestion of fecally contaminated food
or water. The infections from these parasites are usually self-limiting, but among children, the elderly,
and the immunocompromised, the infections can lead to chronic diarrhea, anemia, fever, and possibly
death (Hoxie et al., 1997; US EPA, 1998; CDC, 2002a). In 1979, Giardia was responsible for 2,000
illnesses after backpressure effluent from a tree bubbler system in an Arizona State park (Lake Havasu)
contaminated the potable water supply (USCFCCCHR, 1993). In 1994, dozens of people became ill
from Giardia contamination through a cross-connection between a drain and an ice machine at a
convention in Columbus, Ohio (AWWA PNWS, 1995).
Other contaminants
Biological contaminants that are nonmicrobial can also enter the distribution system. For
example, due to a cross-connection at a funeral home, human blood and bodily fluids from the
embalming process were backsiphoned into the distribution system, and blood flowed from water
fountains and other water fixtures (US EPA, 1989). Human bodily fluids can be a vector for disease as
well as being an aesthetic concern.
5.3 Data on Selected Backflow Incidents, 1970-1999
There are no reporting requirements nationally for backflow incidents, and no central repository
for backflow incident information. Nonetheless, data on backflow incidents have been actively collected
by several organizations, including the following:
• Centers for Disease Control (CDC), the federal agency that tracks epidemiology of illnesses
as reported by doctors and health care providers.
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•	Cross-Connection Control Committee of the Pacific Northwest Section of the American
Water Works Association (AWWA PNWS), a technical and educational association for the
drinking water industry.
•	University of Southern California's (USC's) Foundation for Cross-Connection Control and
Hydraulic Research, a water engineering research and industry standards development
organization.
•	American Backflow Prevention Association (ABPA), a training and advocacy association for
the water system industry.
Drawing from these and other sources, including EPA Regional Offices, the Florida Department
of Environmental Protection, professional manuals on controlling cross-connections, and news reporting
accounts, EPA compiled data on 459 backflow incidents that occurred in the United States between 1970
and 2001. Exhibit 5.1 summarizes the types of incidents reported at various sites and indicates the wide
range of problems that can occur. Because backflow incidents are underreported, the data cannot support
conclusions about the full magnitude of risk associated with backflow. And the exhibit summarizes only
the reported acute health impacts, as surveillance programs do not capture impacts due to chronic
exposures or chronic health effects.
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Exhibit 5.1 Reported Backfiow Incidents for Which EPA Has Compiled Data
Source of
Contamination
Documented
Incidents
Examples of Incidents
Residential Sites
Homes With
Individual
Connections
55
In 1991, an atmospheric vacuum breaker valve intended to
protect a cross-connection between an irrigation system and the
potable supply malfunctioned, allowing backfiow of irrigation
water into the public water system. The water system, located
in Michigan, was contaminated with nematodes, rust, and
debris (AWWA PNWS, 1995).
In 1997, recycled water reached approximately 1,600 California
homes and businesses from a residential connection after a
property owner illegally tapped into a reclaimed water line
(California HHS Agency, 2001).
Apartment
Buildings or
Condomini urns
27
•	In 1981, chlordane and heptachlor were backsiphoned through a
garden hose submerged in a termite exterminator's tank truck in
Pennsylvania. An undiscbsed number of illnesses occurred, and
75 apartment units were affected (NAPHCC, 1996).
•	In 1985, hexavalent chromium backflowed from a Boston,
Massachusetts condominium's cooling tower into the potable
water system (NAPHCC, 1996).
Mobile Homes
or Mobile Home
Parks
1
• In 1984, a leak developed in a wall separating solar water heater
heat transfer medium from a residential water supply. The water
supply of a mobile home in Oregon was contam inated with
dichlorofluoromethane (AWWA PNWS, 1995).
Neighborhood
3
•	In 1995, a business tapped into an irrigation line containing
untreated water in Yakima, Washington, without installing a
backfiow prevention device. This allowed Giardia to contaminate
area residences, resulting in 11 cases of giardiasis. (AWWA
PNWS, 1995).
•	In 1997, a fire truck pump created backpressure on a fire hydrant
before the valve was closed, forcing over60 gallons of aqueous
fire-fighting foam into an estimated 40,000 neighborhood taps in
Charlotte-Mecklenburg, North Carolina (ABPA, 1999).
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Exhibit 5.1 Reported Backfiow Incidents for Which EPA Has Compiled Data
Source of
Contamination
Documented
Incidents
Examples of Incidents
Government and Institutional Sites
Medical Sites
(Hospital,
Dental, Nursing
Sites, Blood
Banks, etc.)
27
•	In 1982 in Illinois, ethylene glycol backsiphoned from an air
conditioning system's water holding tank into a group of dialysis
machines, contributing to the death of "several" (number not
given) patients (AWWA PNWS, 1995).
•	During shut-down of a water main to repair a valve in 1984, the
backfiow of water from a nursing home's boiler caused burns to a
water de partm ent em ployee's ha nds in W ashingto n State
(AWWA PNWS, 1995).
•	In 19 94, d uring repa irs to a nurs ing ho me air co nditio ning u nit in
Franklin, Nebraska, a hole left in the cooling coils allowed freon
to backfiow into the city water main, affecting the city's 1,100
residents. Customers complained about the taste of the water,
but no illnesses were reported (AWWA PNWS, 1995).
Schools,
Universities, and
Child ren's
Camps
31
•	In 1990, six staff members of an Indiana middle school reported
becoming ill after drinking water containing ethylene glycol that
backfiowed from the school's cooling system into the potable
water system (AWWA PNWS, 1995).
•	In 1987, coppersediment contaminatbn in a beverage mixing
tank resulted in four cases of illness in a residence hall at
Michigan university (AWWA PNWS, 1995).
•	In 1995, three people became ill at a California school after
drinking water from a system with a double-check backfiow
prevention valve that did not meet industry standards and had
badly deteriorated rubber gaskets (Craun and Calderon, 2001).
Public Water
Systems
15
•	In 1984, creosote was backsiphoned through a three-quarter inch
hose used to prime a pump, contaminating a section of a
Georgia community watersystem. No illnesses were reported
(AWWA PNWS, 1995).
•	In 1970 in Mattoon, Illinois, hot wash water from an asphalt plant
backpressu red into mains during flow testing of fire hydrants
(USC FCCCHR, 1993).
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Exhibit 5.1 Reported Backfiow Incidents for Which EPA Has Compiled Data
Source of
Contamination
Documented
Incidents
Examples of Incidents
Other
Gove rnment/
Institutional
Sites (e.g.,
public bu ildings,
churches)
24
•	In 1976, water fountains at the State Capitol building in Salem,
Oregon, were contaminated with freon gas from a ruptured heat
exchanger. The gas combined with the fluoride in the water
supply, forming an acid compound that caused a bitter, burning
taste (AWWA PNWS, 1995).
•	In 1991, two check valves froze open at a Texas Air Force base,
resulting in a backfiow from a water chiller; pathogenic bacteria
were detected in the water. The specific contaminant was not
identified. Approximately 22,000 workers and residents were
without water during system flushing (AW W A PNW S, 1995).
•	In 1994, the water system at a Tennessee prison was cross-
contaminated by the facility's wastewater pump station, resulting
in 304 cases of giardiasis (Craun and Calderon, 2001).
•	Purified drinking water lines at the Oak Ridge Reservation's K-25
atomic bomb fuel plant were interconnected foran unknown
length of time (possibly on the order of decades) with lines
carrying impure creek water. The creek water contained poisons
generated from nuclear fuel production, possibly including
contaminants such as strontium-90 and arsenic (Nashville
Tennessean, 2000).
Commercial Sites
Restaurants
28
•	In 1979, two high school students in Seattle, WA, became ill,
showing symptoms of copper poisoning afterdrinking soft drinks
from a dispensing machine in a restaurant. The backfiow of
carbon dioxide from the soft drink dispensing machine was
considered the likely cause of the copper release (AWW A
PNWS, 1995).
•	In 1987, a child in Minnesota suffered acute copper toxicity when
backfiow from a carbon dioxide machine contaminated a
restaurant's potable system (AWWA PNW S, 1995).
Office Buildings
18
•	In 1989, a backfiow event at an Ohio government office building
occurred after crews worked on the air conditioning system.
Twelve individuals became ill after ingesting water that had been
contaminated with Acid Blue 9, an algae-retarding chemical
(AWWA PNWS, 1995).
•	In 1991, trichloroethane entered the distribution system of a city
in Missouri from a newspaper office. Uncoordinated flushing by
the water system caused the contaminant to spread throughout
the system , with concentrations as high as 420 m icrogram s/L
(AWWA PNWS, 1995).
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Exhibit 5.1 Reported Backfiow Incidents for Which EPA Has Compiled Data
Source of
Contamination
Documented
Incidents
Examples of Incidents
Other
Commercial
Sites
66
•	In 1974, backsiphonage of a chromium compound from the
chiller water of an air conditioning system contaminated the
drinking water system in the auditorium hosting the 94th annual
AWW A conference and exhibition in Massachusetts, involving
thousands of peop le (AWW A PNW S, 1995).
•	In 1990, 1,100 guests of a Tennessee racquet and country club
became ill with an intestinal disorder after consuming the club's
contaminated watersupplied from an unauthorized and
unprotected auxiliary well in close proximity to a malfunctioning
sewage pumping station (AWWA PNWS, 1995).
•	In 1994, a number of individuals attending an Ohio conventbn
got sick with giardiasis, spread by an ice machine contaminated
by a cross-connection to a sewage drain (AWWA PNW S, 1995).
Miscellaneous Sites
Agricultural
Sites
6
•	In 1991, an antibiotic solution used at a commercial chicken
house entered an Arkansas public water system as a result of a
cross-connection between an auxiliary well connected to the
chicken house plumbing (AWWA PNWS, 1995).
•	In 1995, pesticides (paraquat and atrazine) were backsiphoned
into a distribution system when an accidental water main cut
occurred while a Louisiana farmer was diluting herbicides in a
tank. Some people reported nausea, stomach burns and pains,
profuse sweating, diarrhea, and shortness of breath. The
incident was the subject of a class-actbn lawsuit (AWWA
PNWS, 1995).
Recreational
Sites
10
•	In 1986 in Springfield, MO, failure of a single check valve on a
soft drink dispensing machine ata local fair resulted in the
backfiow of carbon dioxide that created levels of 2.7 mg/L of
copper and 2.2 mg/L of zinc. Three people experienced vomiting
and abdominal pain (AWWA PNWS, 1995).
•	In 2000, contaminated water lines at an Ohio fairground resulted
in an outbreak of E. coli, resulting in 30 cases of illness
(Cleveland Plain Dealer, 2001).
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Exhibit 5.1 Reported Backfiow Incidents for Which EPA Has Compiled Data
Source of
Contamination
Documented
Incidents
Examples of Incidents
Industrial Sites
40
•	In 1989, backpressure from a propane tank car forced propane
into the water supply of Fordyce, Arkansas. Three people in
separate buildings were injured from explosions after flushing
toilets, and two houses were destroyed and a business was
damaged by expbsions and subsequentfires (AWWA PNWS,
1995).
•	In 1990, at least two individuals became ill after an unknown
quantity of industrial chemicals backflowed into the public water
supply via an unprotected auxiliary line illegally tapped to a hose
connected to the plant's flushing system. The incident occurred
at a New Mexico facility that transforms wheat and barley into
ethanol (AWWA PNWS, 1995).
Other S ites/Site
Type Unknown
108
• In 1980, a cross-connection aboard an Alaskan crab processing
ship resulted in backfbw of sewage (including Giardia), causing
189 employees to become ill and endangering about $35 million
worth of processed king crab (USC FCCCHR, 1993; CDC, 1982).
Total
459

Source: CDC, AWWA PNWS, ABPA, EPA, USC FCCCHR, FDEP, and Newspapers
5.4	Occurrence of Cross-Connections and Backfiow
From a 1999 American Backfiow Prevention Association (ABPA) survey, ABPA estimated that
42 percent of cross-connection surveys conducted (by 135 respondents, representing 30 states) identified
a cross-connection. The most common cross-connections reported were from irrigation (62 percent of
respondents identified an irrigation cross-connection), fire systems (43 percent), garden/washdown hoses
(43 percent), and boilers (38 percent). A total of 233 backfiow incidents were reported by 51 percent of
respondents, or 1.7 incidents per system (ABPA, 1999). These numbers only reflect those backfiow
incidents detected; many go undetected because it is not practical for systems to continuously monitor
their distribution systems for changes in pressure or the presence of contaminants. In addition, ABPA
conducted a survey in 2000, which included a question on the occurrence of low pressure events which
may lead to backfiow where unprotected. A survey of 70 systems responding to the survey reported
11,186 pressure reduction incidents in the previous year; 34.8% of the incidents were from routine
flushing, 19.2% were due to main breaks, and 16.2% of the incidents were due to service line breaks
(ABPA, 2000).
5.5	Difficulties in Detecting Backfiow Incidents and Assodated Outbreaks
Contamination due to backfiow incidents may not be detected or reported for several reasons:
• Bacterial contamination tends to be transient and highly localized (ABPA, 1999).
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•	Water system operators monitor routinely for coliform bacteria, however, most often that is
the only microbial monitoring conducted (US EPA, 2001). While these bacteria are
important indicators of distribution system problems, some microbial contaminants may go
undetected. The limited nature of biological monitoring, especially in smaller systems (as
infrequent as once per year), makes it unlikely that contamination will be detected in a
timely manner. Operators monitor for a limited number of chemicals (US EPA, 2001), but
not routinely or often enough to identify most backflow incidents.
•	Most backflow incidents are generally detected and reported to the local authority only if
customers detect an irregularity in their water supply. Not all contamination that produces
illness and disease can be detected by taste, color, or odor (Hoxie et al., 1997). For many
highly toxic substances, including benzene, vinyl chloride, and dichloromethane, the taste
and odor threshold is well above the drinking water maximum contaminant level (MCL)
(DWI0441, 1992; Glaza and Park, 1992).
•	Even if an irregularity is detected, it may not be reported by the consumer.
•	When water system operators suspect backflow incidents, they have a disincentive to
document and report them because of concerns about legal liability and loss of consumer
confidence, as noted by an EPA Office of the Inspector General report (US EPA, 1995).
(Fortunately, these same concerns provide the utility with an incentive to protect the
distribution system.)
•	The difference between epidemic and endemic transmission is obscured by limitations in
recognizing when an outbreak occurs (Frost et al., 1996). A study of waterborne
cryptosporidiosis estimates that out of every 10,000 infections by Cryptosporidium only 3
would be reported, and concludes that surveillance for detected cases of a reportable illness
may substantially underestimate rates of infection and morbidity (Perz et al., 1998).
•	Some contaminants that enter the distribution system through cross-connections and
backflow may not be reportable.
•	The incidents of reduced pressure and some cross-connections are often transient in nature.
Pressure changes may not be detected by conventional pressure monitoring equipment.
Reduced pressures may also affect only a portion of the distribution system, a specific
pressure zone, or only piping beyond the service connection.
State officials offer perspective on the estimated extent of underreporting. One State official
suspects that there may be 10 times as many as incidents as are reported (Fauver, 2002). Another State
official estimates approximately 1,200 backflow incidents occur per year, assuming that all water main
breaks will cause a backflow incident (and each of 600 public water systems in the State average 2 water
main breaks a year). Yet only 15 backflow incidents have been documented in the State since 1970
(Koenig, 2002).
Outbreaks of illness associated with backflow incidents also are underreported, for the following
reasons:
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•	Outbreaks of illness may not be linked to an incident of backflow contamination (Craun and
Calderon, 2001). Documented effects of contamination are usually acute and result from
short-term exposures; whether mild or severe, the effect appears soon after exposure. Effects
that are long-lasting or only appear after some time (chronic effects) are difficult to ascribe
to a single event or associate with a waterborne source. Cross-connections combined with
uncorrected backflow situations that cause continuous or intermittent exposure over a long
time and result in chronic illness would be less likely to be linked to backflow
contamination.
•	Contamination may not affect enough people to attract the attention of public health officials
(Craun and Calderon, 2001).
•	Information that could tie an incident to an outbreak of illness or disease, such as where and
when a contaminant entered the system, is often missing.
Even when incidents are detected and voluntarily reported, inconsistent reporting and
documentation procedures make it hard to assess the full scope of the problem Some organizations that
record incidents will accept reports only if they have documentation that meets their standards. The USC
FCCCHR prepared a Summary of Case Histories (USC FCCCHR, 1993) that covers 397 incidents from
1903 to 1993. The Chief Engineer of the Foundation estimated that more than 90 percent of the
backflow incidents known to water system administrators were not documented enough to be included in
the case histories (CCC WS, 1999). Inadequate documentation can result from the fact that where
backflow is suspected, in most instances it is difficult if not impossible to trace the origin of
contamination (BMI, 1999).
6.0 Costs of Backflow Contamination Incidents
The costs associated with backflow incidents depend on the nature and scope of the incident and
the nature and extent of the response. Depending on these factors, costs could be incurred for public
notification; the repair of damage to water distribution system infrastructure; investigation, sampling, and
laboratory analysis; clean-up of structures and equipment; purchases of bottled water; responding to
consumer complaints; lawsuits (both legal fees and judgments); the repair of property damage;
replacement of spoiled food; missed work and school; loss of production; and medical expenses. Beyond
actual costs, other losses could include leisure time and even mortality.
The ABPA 1999 survey gathered information to estimate the costs water systems may incur to
mitigate a backflow incident. The survey collected data from 25 water systems serving fewer than
10,000 people and from 103 systems serving 10,000 people or more. Survey results show that for the 92
systems that responded, water system operators expended an average of 494 hours per event mitigating
backflow incidents. At $30 per hour (the average rate of technical labor reported by the Bureau of Labor
Statistics (2000)), that averages $14,800 per event. Eleven of these were significantly more time
consuming than the others, averaging 3,683 hours and about $110,500 (at $30 per hour) per incident.
Excluding these 11 most time-consuming incidents, operators expended an average of 60.8 hours per
incident and $1,820 per incident. Utility-level costs such as these do not include costs for all of the
possible elements described earlier, especially those for health-related effects.
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Other backflow incidents reported monetary losses due to food spoilage, property damage, and
lawsuits. Examples include a backflow of wastewater through a cross-connection created with the water
supply and the wastewater line when a new well was installed; the wastewater contaminated pork valued
at approximately $2 million (NAPHCC, 1996). A lawsuit for $21 million was filed against a pest control
company that contaminated the water supply to 63 homes and businesses with pesticide; the money was
compensation for physical distress, inconvenience (the homes and businesses were without water for
several days), and loss of property value (AWWA PNWS, 1992).
7.0 Other Problems Associated with Backflow Incidents
This section discusses other negative effects associated with cross-connections and backflow
that, although not a direct threat to health, can cause other undesired effects such as negative publicity,
consumer complaints, damage to the water system, and impediments to system operation. Negative
effects discussed are: 1.) corrosion; 2.) microbial growth; and 3.) taste, odor, and color problems.
Corrosion
Many contaminants, such as acids and carbon dioxide, can corrode pipes and other distribution
system materials. Many incidents of corrosion induced by carbon dioxide backflow have released toxic
amounts of copper into drinking water systems (AWWA PNWS, 1995). Many of these incidents were
reported because the corrosion was rapid enough and large enough in extent to produce concentrations of
corroded metal high enough to be toxic or to lead to complaints about taste and odor.
Corrosion in iron pipes is much less likely to be noticed because iron is not as toxic as copper,
and corrosion of iron and steel is relatively slow, leading to lower concentrations. But slow corrosion is
a problem: corroded iron pipes can lead to discolored water, stained laundry, and taste complaints
(McNeil and Edwards, 2001). Corrosion can also weaken the integrity of pipes, causing leaks that can
allow contaminants in through intrusion or catastrophic breaks, which can in turn cause reduced pressure
(McNeil and Edwards, 2001). Corrosion of iron pipes can also form tubercles that can shelter microbes
(including pathogens) from disinfection (US EPA, 1992).
Microbial growth
When backflow through cross-connections introduces microbes into the distribution system,
these organisms can attach to pipe walls in places where the disinfectant residual may be inadequate to
inactivate the microbes, such as in dead ends. Such organisms, even if they are not pathogenic
themselves, can be a concern because they can colonize on the pipe walls, forming biofilms (US EPA,
1992) that trap and concentrate nutrients, promoting growth of pathogens (Costerton and Lappin-Scott,
1989). The bio film can lead to total coliform violations, even in the absence of contamination events.
Bio film can also cause complaints about taste and odor and harbor potentially pathogenic organisms from
disinfection (Characklis, 1988). Backflow through cross-connections can also introduce nutrients that
support the growth of pre-existing biofilms.
Taste, odor, and color problems
Some contaminants introduced through cross-connections and backflow may not cause illness
but may result in consumer complaints about the tastes, odors, or color of the water (e.g., seawater and
dyes (AWWA PNWS, 1995)). Such incidents can lower consumer confidence in the water system,
require water and employee time to flush the system to remove the offending contaminant, and initiate an
investigation to identify and correct the cross-connection.
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8.0 Suitable Measures for Preventing and Correcting Problems Caused by
Cross-Connections and Backflow
This section reviews existing research, data, and available information regarding the prevention
of cross-connections and backflow incidents, as well as mitigation measures systems use following a
backflow incident.
8.1 Preventive Measures
Backflow into the public water distribution system can be prevented by eliminating cross-
connections or protecting the potable water supply using backflow prevention devices and assemblies.
Some systems educate the public to prevent cross-connections, and maintain and inspect the distribution
system to correct those found. However, because situations frequently arise where new cross-connections
occur before they are detected and corrected, it is helpful to build in to the distribution system physical
impediments to backflow, including mechanical backflow prevention devices and assemblies. Systems
look to minimize the risk posed to their distribution systems from a customer's plumbing system, and
therefore conduct hazard assessments in order to determine the level of protection needed and what
approach should be taken. The appropriate type of protection depends on the physical characteristics of
the cross-connection (e.g., whether there is a potential for backpressure in addition to backsiphonage) and
the degree of the potential hazard. The degree of hazard is a function of both the probability that
backflow may occur and the toxicity or pathogenicity of the contaminant involved. A high hazard can be
defined as,
"a condition, device, or practice which is conducive to the introduction of waterborne disease
organisms, or harmful chemical, physical, or radioactive substances into a public water system,
and which presents an unreasonable risk to health" (BMI, 1996).
Low hazard can be defined as,
"a hazard that could cause aesthetic problems or have a detrimental secondary effect on the
quality of the public potable water supply" (BMI, 1996).
Another reason for conducting risk assessments is to determine and help manage legal liability
due to public health risk; therefore, these definitions of high and low hazard are ultimately subjective and
depend upon the risk aversion of the water system, appropriate local regulations, and the particular risk
assessment conducted by the system.
8.1.1 Physical Separation
Air gaps, if designed and maintained properly, make backflow physically impossible as they
ensure that there is no connection between the supply main and the nonpotable source. An effective air
gap is a physical separation of a supply pipe from the overflow rim of a receiving receptacle, by at least
twice the diameter (minimum of one inch) of the incoming supply pipe (USC FCCCHR, 1993; BMI,
1996). The distance between the end of a faucet and the overflow of a utility sink is an example of an air
gap. While air gaps provide physical assurances against backflow, they are often tampered with as
people extend the end of the pipe to prevent splashing and thus potentially create a cross-connection. By
the AWWA standard, air gaps are acceptable in lieu of mechanical backflow prevention assemblies
beyond the service connection only if installed and maintained by the local cross-connection control
program enforcement agency (AWWA, 1999).
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8.1.2 Backflow Prevention Devices and Assemblies
Mechanical backflow prevention devices and assemblies offer protection of the potable water
system if other protective approaches fail. Backflow prevention devices and assemblies may be installed
at the service connection to a facility (effectively "containing" a potential contaminant within a
customer's plumbing system and preventing it from entering the distribution system). Alternatively,
devices and assemblies can also be installed at high and low hazard cross-connections inside the facility,
including all outlets where cross-connections could potentially be created (this type of approach is called
"isolation" or "fixture outlet protection"). Some drinking water authorities prefer isolation to
containment because personnel working beyond the service connection are protected and, in most cases,
the assembly can be sized smaller because of smaller piping beyond the service connection. However,
backflow devices and assemblies used for isolation could be bypassed through changes to internal
plumbing, inadvertently creating an unprotected cross-connection
There are two types of mechanical protection available to systems: backflow prevention
"devices" and backflow prevention "assemblies". Backflow prevention devices function by stopping the
reversal of flow, but are not testable once installed because they do not have inlet and outlet shut-off
valves or test cocks (USC FCCCHR, 1993). Backflow prevention assemblies, by contrast, include an
inlet and outlet shut-off valve and test cocks to facilitate testing of the assembly while it is in its
functional environment (in-line) (USC FCCCHR, 1993).
Backflow prevention assemblies include pressure vacuum breakers (PVBs), spill resistant
vacuum breakers (SVBs), double check valve assemblies (DCVAs), and reduced pressure principle
backflow assemblies (RPs) (USC FCCCHR, 1993) (BMI, 1996). PVBs are vertically positioned
assemblies that include spring-loaded check valves designed to close when flow stops (USC FCCCHR,
1993). They also have an air inlet valve that is designed to open when the internal pressure is lower than
the atmospheric pressure, preventing backsiphonage but not backpressure. PVBs must be a minimum of
12 inches above all downstream piping and the flood level rim of a receptor to function properly. PVBs
are designed to protect against low- or high-hazard situations.
SVBs are similar in design to PVBs with the addition of a diaphragm seal that stops water from
spilling out the air inlet whenever the assembly is pressurized. As with PVBs, they protect against
backsiphonage only (BMI, 1996).
A DCVA consists of two internally loaded, independently operating check valves together with
tightly closing resilient seated shut-off valves upstream and downstream from the check valves (USC
FCCCHR, 1993). These assemblies require a minimum of 1 foot of clearance at the bottom for
maintenance purposes to allow for the worker to get to the assembly. These assemblies are used for
protection against either backsiphonage or backpressure, but only for situations of low hazard.
RPs consist of two internally loaded, independently operating check valves and a mechanically
independent, hydraulically dependent relief valve located between the check valves (USC FCCCHR,
1993). The relief valve maintains a zone of reduced pressure between the two check valves. The RP
also has tightly closing, resilient seated shut-off valves upstream and downstream of the water supply.
RPs must have a minimum of 1 foot clearance at the bottom of the assembly for maintenance purposes.
RPs protect against backsiphonage or backpressure in low- or high-hazard situations.
One common backflow prevention device is an atmospheric vacuum breaker (AVB). AVBs rely
on atmospheric instead of water pressure to work, and are installed downstream from all shut-off valves.
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AVBs contain an air inlet valve that closes when the water flows in the normal direction. But, as water
ceases to flow, the air inlet valve opens and prevents backsiphonage. AVBs must be a minimum of 6
inches above all downstream piping and the flood level rim of a receptor to function properly (USC
FCCCHR, 1993). Household hose bib vacuum breakers and frost-proof wall hydrant faucets are
examples of AVBs. According to some, AVBs do not protect against backpressure and are used in
situations of low hazard (BMI, 1999); however, some plumbing codes recognize AVBs as high hazard
assemblies.
The selection of any particular assembly or device is a function of the hazard assessment that
balances the likelihood of backpressure and backsiphonage and the potential contaminants involved. The
total cost of installing and maintaining a particular device or assembly can also be a factor for some
water systems. In cases of low hazard and backsiphonage only, systems typically install less expensive
AVBs or PVBs. If backpressure is a concern, many systems use double check valve assemblies, and if
the degree of hazard is high, many systems install a reduced pressure principle backflow assembly.
The cost of backflow preventers has been reported by industry experts to be a deterrent in
starting and maintaining and backflow prevention program (CCC WS, 1999). The cost of backflow
preventers can range from $18 to over $22,000 (Watts, 2002), depending on the size and preventer type.
Installation costs are typically borne by the water system and passed along to consumers, or are borne
directly by consumers (ABPA, 2000).
8.1.3 Cross-Connection Control and Backflow Prevention Programs
Many states and local jurisdictions require cross-connection control and backflow prevention
programs. However, many utilities do not have programs, or have programs that are insufficient to
provide reasonable protection from cross-connections (ABPA, 1999). The program requirements vary
widely between states: they may be part one or more of various regulations, including the drinking water
regulations, health code, plumbing code, policy decision of the utility itself and building codes. A 1993
U.S. General Accounting Office report on the review of 200 sanitary surveys and a nationwide
questionnaire of states identified inadequate cross-connection control programs as the most common
deficiency (US GAO, 1993).
Programs and their level of effort are often tailored to the perceived risk of backflow and the
types of hazards that can be introduced into the distribution system (USC FCCCHR, 1993). These
factors may contribute to determining whether a containment or isolation program is implemented
locally, as well as what types of backflow preventers are required. The need for backflow prevention in a
water system is determined through a variety of means, including: surveys of new sites; retrofit
programs; and change of occupancy inspections. Some programs inspect a site upon request. In many of
these cases, identification of hazards determines the need for backflow prevention For example, Kansas
City, Missouri's program does informal, informational checks and passes the data to the plumbing
authority (Nelson, 1999). The cross-connection control programs of Boston and Cambridge,
Massachusetts, check connections to the last free-flowing tap (Hendrickson, 1999). Other programs,
such as the one for Gatlinburg, Tennessee, identify additional requirements as a function of the risk of
the facility (City of Gatlinburg, 2001). The water system in Price, Utah, performs about 20-30
inspections each year, about half of which go beyond containment to focus on potential cross-connection
hazards. Staff focus primarily on high-hazard sites, but inspect other types of sites after installations or
upgrades (Price, 1999).
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In an effort to evaluate the measures states take to address cross-connections and backflow, EPA
analyzed existing state requirements (Exhibit 8.1). The analysis reviewed regulations of all states
pertaining to drinking water, clean water, and plumbing and building codes. Additionally, information
from the following surveys was used as supplementary information for the analysis: the EPA Office of
Inspector General Report (The Survey Report on the Cross-Connection Control Program, 1995); the
Florida Report (The State of Florida's Evaluation of Cross-Connection Control Rules/Regulations in the
50 States, FDEP, 1996); Governmental Affairs Committee (GAC) Follow-up Survey (Summary of the
Cross-Connection Control Requirements-Nationally, 1997); the American Backflow Prevention
Association (ABPA) Survey, 1999; the Association of State Drinking Water Administrators (ASDWA)
Survey, 1999; and the Van Loon Survey, 1999.
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Exhibit 8.1. State Cross-Connection Control Requirements
Requirement
Number of States
With Requirement
Does the State have a requirement for the control of cross-connections and/or
backflow prevention?
50
Is it specified in the requirement that the system must implement or develop a
cross-connection control and/or backflow prevention program?
32
Does the State require authority to implement a local ordinance or rule for cross-
connection control and/or backflow prevention?
33
- Must the authority cover testing of backflow prevention assemblies?
27
- Must the authority cover the use ofonly licensed or certified
backflow assembly testers?
16
- Must the authority cover the entry of the premises for the sake of
inspecting the premises?
14
- Must the authority cover the entry of the premises for the sake of
inspecting and/or installing backflow prevention assemblies?
15
Does the State require training, licensing, or certification of backfbw prevention
assembly testers?
26
Does the State require training, licensing, or certification of backflow prevention
assembly and/or device installers?
6
Does the State require training, licensing, or certification of backflow prevention
assembly and/or device repairers?
10
Does the State require training, licensing, or certification of cross-connection
control inspectors?
19
Does the State require inspection of backflow prevention devices and/or testing of
backflow prevention assemblies?
37
Does the State require the system to include record keeping as part of cross-
connection control?
34
Does the requirement include keeping records of hazard assessment surveys?
11
Does the State require the system to notify the public following the occurrence of a
backflow event?
3
Does the state require the local rule or ordinance to allow the system to take
enforcement action against customers that do not comply with the cross-
connection control and backflow prevention requirements?
23
Does the State conduct periodic reviews of cross-connection control programs?
3
Does the State regulation or plumbing code require public education regarding
cross-connection control and/or backflow prevention?
7
Source: Derived from state drinking water and clean water regulations and state plumbing and building codes.
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Considerable variability exists in state statutes, regulations, and policies related to cross-
connection control and backflow prevention In some cases where states do not require programs, some
water systems within the state have implemented comprehensive and active programs in absence of a
state requirement to do so.
According to input from a Cross-Connection Control Expert Meeting in September, 1999, a
program is considered active and comprehensive if it contained regulations with these requirements: 1)
require adoption of some form of legal authority (ordinance, by-law, code) for establishing and
maintaining a cross-connection control program at the local level; 2) require training and certification
specifications; 3) require record keeping and reporting; 4) provides public education; and 5) define
enforcement responsibility and penalties. Many state programs that require cross-connection control and
backflow prevention programs share these elements (ASDWA, 1999; USC FCCCHR, 1993). As noted
in Exhibit 8.1, several states have these requirements, although a majority do not have all five of the
recommended minimum elements.
Authority
Experts agreed that a cross-connection control program should have the authority to effectively
enforce its ordinances and requirements (CCC WS, 1999). It is recommended by groups such as the
AWWA (AWWA, 1999) that local cross-connection control programs have the legal authority in place to
carry out basic program requirements, such as: 1) enter premises and inspect facilities to determine the
degree of hazard and the presence of cross-connections; 2) to install, repair, and test backflow devices; 3)
license employees or contractors engaged in testing of assemblies to ensure competency; and 4)
terminate water service in case of noncompliance. Not all states require authority to effectively enforce
the ordinances and requirements—33 states require local authorities to implement cross-connection
control ordinances. Of those states, only 14 states require authority to enter premises for inspection
purposes, and 15 states require authority to enter premises to inspect or install backflow prevention
devices (Exhibit 8.1).
Different local authorities may have pre-existing responsibilities that would be overlapped by a
cross-connection control program. Water utilities typically have the responsibility to protect the
distribution system up to a customer's meter. In some cases, they fulfill this responsibility by placing
backflow assemblies at the meter (USC FCCCHR, 1993). Plumbing authorities are often responsible for
all potable water connections downstream of the meter (USC FCCCHR, 1993). Engineers and building
authorities have inspection and compliance responsibilities which, in some cases, overlap with plumbing
authorities. Additional overlap of authority occurs with regard to fire lines. While fire lines can use
potable water and are frequently interconnected with the potable system (AWWA, 1999), they are
usually unmetered and typically not considered part of the drinking water supply, and therefore are not
subject to plumbing codes. Having backflow assemblies on fire lines (e.g., the Boston, Massachusetts,
program involving the fire authorities) requires the cooperation of fire departments. In addition, many
programs require customers to understand the dangers of backflow and take effective measures to
eliminate, fix, and isolate cross-connections.
Training and certification
Training and certification is considered an important element of a cross-connection control and
backflow prevention program (CCC WS, 1999). The training and certification can cover administering a
program, conducting site surveys, installing and testing approved backflow assemblies, as well as for
maintaining and repairing backflow assemblies. The testing of backflow prevention assemblies by a
certified tester works to ensure that the assembly is functioning properly and will prevent backflow.
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Twenty-six states require certification of backflow assembly testers (Exhibit 8.1). In some states,
backflow assembly testers also install and repair the backflow preventers, however only 6 states require
training, licensing, or certification of backflow installers (Exhibit 8.1). A small number of states expand
their training requirements to program managers, installers, and/or repairers. Nineteen states require
certification of survey inspectors (Exhibit 8.1).
Having trained and certified testers may contribute to effective cross-connection control and
backflow prevention. For example, in 1998, a 42-inch water main broke in close proximity to the Boston
Public Library, causing a dramatic drop in pressure in a large portion of the city for a short period;
however, there were no reported backflow incidents (Hendrickson, 1999). The key elements of the
Boston, Massachusetts, cross-connection control and backflow prevention program include 11 full-time
cross-connection control staff employees, all of whom are certified testers licensed by the State of
Massachusetts (Hendrickson, 1999).
Public education
There have been incidents of water system customers installing inadvertent cross-connections
leading to backflow incidents. Education of the public may reduce the number of cross-connections
created on the customer side, and is therefore a critical element in the implementation and success of a
cross-connection control and backflow prevention program (CCC WS, 1999). Seven states required
public education regarding cross-connection and/or backflow control and prevention (Exhibit 8.1).
Public education is usually a function of the local water purveyor. Also, states sometimes provide
materials for distribution, and maintain Internet sites that include information about state water quality
programs to educate consumers about CCC programs and the role they play in protecting their drinking
water. The Michigan Backflow Prevention Association has developed a video used for training utility
personnel on educating the public (MBPA, 1997).
Educational tools used by local programs are: meetings, brochures, and seminars. Las Vegas,
Nevada, has run multiple seminars to explain the program since they serve two jurisdictions (Blish,
1999). They have been so successful that some of the large casinos now have their own on-site trained
and certified cross-connection control personnel. Tucson, Arizona distributes backflow prevention
brochures to customers, and in the past has used public access television to promote the program. They
also distribute backflow prevention brochures to existing customers during inspections (Adams, 1999).
Other programs distribute fliers and bill inserts. The public awareness program of Sandy City, Utah,
consists of fact sheets, manufacturer's information on backflow prevention, newspaper articles and
newsletters, public meetings with customers, and backflow information provided to people requesting
information on sprinkler systems (Oakeson, 1999).
Reporting and record keeping
A requirement to report backflow incidents is important for detection and correction of cross-
connections (CCC WS, 1999). Although many backflow incidents are believed to occur undetected,
those that are detected can provide valuable information on other potential cross-connections in the
distribution system. Three states require reporting of backflow incidents to the public, while eight states
require systems to notify state authorities (Exhibit 8.1).
Lack of records or poorly organized records can inhibit corrective measures. Thirty-four states
require some sort of record keeping as part of their cross-connection control and backflow prevention
program (Exhibit 8.1). As part of its cross-connection control program, Tucson, Arizona, has a data
management system that tracks each assembly's compliance status (Adams, 1999). The Charlotte-
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Mecklenburg incident involving fire fighting foam, which took 39 hours and 100 city employees to
remedy, prompted the state to require a comprehensive evaluation of the Charlotte-Mecklenburg Utility
Department's backflow prevention program by an outside consultant. One of the key findings resulting
from the evaluation was that the program did not have a formal retrofit program for existing connections
and devoted excessive resources to record keeping; the resources spent on record keeping were used
inefficiently. Since then, the utility has implemented a new data management system to reduce the
record keeping burden and plans to hire an additional staff member to focus on developing a program for
retrofitted equipment (ABPA, 1999).
Testing and repair
Many systems that have cross-connection control and backflow prevention programs require
testing to ensure that backflow preventers are working correctly. As in any mechanical device, backflow
assemblies can deteriorate and fail as they get older. Testing intervals typically are annual, semi-annual,
or risk-based (USC FCCCHR, 1993).
Many states require in regulation or code specific components that make up a testing program.
A testing program frequently identifies the appropriate standards that a backflow prevention device or
assembly must meet (e.g., standards set by the USC FCCCHR, AWWA, or in the Uniform Plumbing
Code (UPC)), as well as specifies a routine testing frequency to ensure adequate performance of the
devices. In many cases, assemblies are then tested by a certified backflow assembly tester.
Approximately 37 states require inspection and/or testing of various backflow assemblies in their
regulations (Exhibit 8.1).
In Boston, Massachusetts, as required by the state, reduced pressure backflow assemblies are
tested twice a year; double-check valve assemblies are tested once per year (Hendrickson, 1999). The
program performs 11,000 site inspections per year. All surveys go to the last free-flowing outlet
regardless of whether the facility is considered high- or low-hazard, as required by state cross-connection
control regulations. Under this program, 100 percent of all high-hazard sites have installed protection.
This high level of testing has prevented any cross-connection incident since 1984, and no boil-water
notices have been necessary (Hendrickson, 1999).
Enforcement
AWWA recommends that cross-connection control program authority should include clearly
defined enforcement procedures such as provisions to shut off water service if devices are not installed or
tested, entry to property is not allowed, devices and assemblies are not installed properly, devices are not
tested, and testing payments are not received (AWWA, 1999). According to the 1995 EPA Office of
Inspector General report, state officials indicated that they adopted a regulation prohibiting cross-
connections and required the local water suppliers to establish a program with the responsibility to
administer and enforce the program at the local level (US EPA, 1995). State officials indicated,
however, that there is little follow-up or enforcement at the state level (US EPA, 1995). In addition,
several states do not require systems to develop programs to implement or enforce the requirements,
through additional drinking water regulations, plumbing codes, or health codes. For example, only 23
states require enforcement action against noncomplying customers (Exhibit 8.1). In Denver, Colorado,
enforcement consists of notifying customers that backflow assemblies must be installed. Customers are
then given 90 days to comply, followed by a second notice, 30 days of grace, and then third notice.
Failure to comply may lead to suspension of water service. Inspections are done by request and number
approximately 25 per month (Stevens, 1999). Thirty-two states require water systems to have a CCC
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program, but only three states conduct periodic reviews of cross-connection control programs, and these
reviews are conducted annually (Exhibit 8.1).
8.1.4	Disinfectant Residual
While not able to prevent cross-connections or backflow from occurring, the use of disinfectant
residuals (i.e., free chlorine or chloramines) can provide a measure of protection against waterborne
disease through the inactivation of some microbial or oxidation of some chemical contaminants.
Although contamination from cross-connections and backflow may be controlled by a disinfectant
residual (Snead et al., 1980), some water supply professionals believe a disinfectant residual is not
effective when cross-connections result in massive contamination (LeChevallier, 1999). In some cases,
reductions in a disinfectant residual can signify the existence of a contamination problem in the
distribution system, including those resulting from cross-connections and backflow (Haas, 1999).
However, some disinfectant residual sampling strategies (e.g., grab samples), may not be able to detect a
reduction in disinfectant residual concentrations for transient events, such as many backflow incidents.
8.1.5	Pressure Stabilization and Maintenance of Positive Pressure
Since backsiphonage and possibly backpressure are induced by drops in distribution system
pressure, maintaining positive and stable pressure reduces the risk of backflow. Minimizing pressure
spikes through use of variable speed pumps and proper valve opening and closing procedures may reduce
the frequency of main breaks that cause backsiphonage (Kirmeyer et al, 2001), and thus be a preventive
measure. Maintaining positive pressure through changes in pumping patterns and adding additional
pump power can minimize backsiphonage and may reduce the occurrence of backpressure events
(Kirmeyer et al, 2001). Pressure stabilization and pressure maintenance maybe difficult for systems
with multiple entry points and those with large variances in elevation or daily demand. Main breaks,
firefighting demands, or other unusual demands that cannot be predicted will also hinder a system's
ability to maintain pressure.
The initial design of a distribution system can minimize possible cross-connection and backflow
opportunities by avoiding low pressure areas and ensuring positive pressure throughout the system.
Water systems that are aware of pressure drops within their distribution systems can conduct additional
water quality testing to determine if a backflow incident has occurred, thus detecting incidents that may
have gone undetected. Systems that have records of pressure over a period of time have the ability to
identify chronic trouble spots, and the records can provide information to devise a strategy to fix them
(LeChevallier et al, 2001). Studying and correcting low pressure zones in existing systems, either
continual or transient, can reduce the number of backflow incidents (LeChevallier et al., 2001).
8.1.6	Pipeline Maintenance and Inspection
Regular inspection of pipelines may identify conditions that could lead to main breaks such as
frozen valves, advanced corrosion, and small leaks, and allow them to be repaired before they lead to
main breaks, which can lead to backsiphonage. Regularly cleaning and flushing pipelines may also
reduce buildup and growth of biofilms that may promote corrosive conditions that can cause pipeline
leaks and eventually breaks (Shindala and Chisolm, 1970; Norris and Ryker, 1987).
8.1.7	Sanitary Surveys
Through the course of conducting sanitary surveys on elements related to the distribution system,
likely cross-connections may be identified and corrected by the water system (US EPA, 1999). Sanitary
surveys may also find evidence of corroding pipelines, frozen valves, and other situations that could lead
to pressure maintenance problems.
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8.1.8 Standards and Codes
The plumbing codes adopted by states are represented in Exhibit 8.2. In addition to the
plumbing codes listed in the exhibit, AWWA also provides guidelines and standards (A WW A, 1999).
Some areas of the country use plumbing codes to set standards, as well as cross-connection control and
backflow prevention programs. The plumbing standards used by many localities can be found in the
Uniform Plumbing Code, the International Plumbing Code, the Building Officials and Code
Administration, and the Southern Building Code Congress International. However, plumbing codes are
often only enforceable against plumbers and property owners, and not public water systems themselves.
Exhibit 8.2 Plumbing Codes Adopted by States
Plumbing Code
Number of States
Adopting
Statewide Code
47
No Statewide Code
3
Statewide Codes Adopted
Uniform Plumbing Code
14
State Code
7
International Plumbing Code
5
National Standard Plumbing Code
4
Southern Building Code Congress
International
4
Other
13
Source: NAPHCC Survey (1999), IAPMO Plumbing Code Adoption Map (2001)
8.2 Corrective Measures
This section describes methods used by water systems to correct contamination from cross-
connection and backflow incidents once they have been detected, as well as minimize resulting
problems. Corrective actions that systems conduct following detection of an incident include: 1)
isolation of the contaminated area; 2) public notification; 3) flushing and cleaning the system; and 4)
pipeline replacement.
8.2.1 Isolation of the Contaminated Area
If preventive measures fail and a backflow contamination event occurs, systems frequently
respond by trying to limit the damage and remove the contaminant from the system. When a system
learns of a contamination event, many systems isolate the portion of the system that was contaminated to
prevent the contamination from spreading. The response to a 1982 propane gas leak in a town in
Connecticut was to first evacuate residents and seal off the affected area (AWWA PNWS, 1995). This is
achieved by shutting off valves surrounding the contaminated area. Crews generally start at the point
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where the contamination was reported and work their way out until they find the edge of the
contamination. Contaminants that are not detectable through sight or smell may be difficult to track and
contain if field testing techniques for the contaminant are not available. Because a stuck valve can
prevent an area from being isolated and lead to the spread of contamination, valve exercising programs
can be important in isolating contamination events. In 1988, in response to a backflow incident at a paint
factory in Edgewater, Florida, the factory manager isolated the factory water system from the city water
system prior to flushing out the contaminants (USC FCCCHR, 1993). An example of not being able to
isolate the area is the Charlotte-Mecklenburg incident (Exhibit 5.1), which required 90 million gallons to
flush the distribution system (ABPA, 1999).
8.2.2	Public Notification
If a contamination event has occurred and the contamination was unable to be isolated before
reaching customers, all customers served by the system must be notified (65 FR 25982). The type of
notification depends on the contaminant and the size of the area contaminated (65 FR 25982). If the
contaminant has acute health effects notification must be as quick as possible, either through broadcast
media or through system employees or public safety officials going door-to-door depending on the size
of the area. For contaminants without immediate or short-term health effects, the public can be notified
by other methods such as letters placed in mail boxes or print media (65 FR 25982). Notification of the
public can prevent health effects by minimizing possible contact with contaminated water until other
immediate corrective measures have been completed. During the Charlotte-Mecklenburg incident
(Exhibit 5.1), the city coordinated an emergency response and notified 40,000 affected customers. In a
25-block radius from the incident, door-to-door notifications were made instructing customers not to use
their water. An extended area beyond the door-to-door radius was notified through media reports not to
use their water (ABPA, 1999).
8.2.3	System Flushing and Cleaning
Once a contamination event has been detected and isolated, usually water system authorities
flush the system as a first attempt to remove the contaminant. Flushing is done by opening up hydrants
and expelling water from the system using a wide open valve approach until the contaminant can no
longer be detected. If a large area has been affected several hydrants may need to be opened in
succession to clean the system. Flushing generally moves from the source of contamination in the
downstream direction. If the source of contamination is not found and fixed there is a possibility of a
repeat incident In 1986, after sodium hydroxide contaminated the distribution system of Lacey's
Chapel, Alabama, water mains and affected plumbing were flushed after containment (Watts, 1998).
Valves are then slowly opened before the hydrant is turned off. This allows for the removal of any
contamination that was undetected during system isolation and may have moved beyond the valves used
for isolation (Yoke and Gittelman, 1986). Out of 28 backflow incidents on which EPAhas information
and where a response was reported, 12 reported flushing the affected portion of the distribution system.
Some contaminants may not be adequately removed by flushing. Microbial contaminants may
concentrate in biofilms that may not be easily dislodged by flushing alone. The water system serving
Muncie, Indiana, drained its entire distribution system over a weekend in an unsuccessful effort to
remove the biofilm (Geldreich, 1996). Other contaminants may adsorb to biofilm layers or corroded
pipe materials and be released slowly to water in the pipe and, therefore, may take an unreasonable
amount of time to flush from the system (US EPA, 1992). In these cases, water systems may opt to
physically clean the pipelines. Pigging and rodding are cleaning methods where a device is introduced
into the pipe that physically scrapes biofilm and corrosion layers from the sides of the pipe (Kirmeyer et
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al, 2001). Jetting and sandblasting can also be used to remove such layers. Typically pipes are
disinfected and flushed after a physical cleaning by one of the above methods.
8.2.4 Pipeline Replacement
Some contaminants may not be removed by physical cleaning. Examples include the pesticide
chlordane, which can adsorb to even clean pipe material and is released into solution only at slow rates.
In 1987, following contamination of drinking water lines in Fairlawn and Hawthorn, New Jersey, with
the pesticides chlordane and heptachlor, the affected lines were removed and replaced (AWWA PNWS,
1995). Radioactive materials are also difficult to remove physically as they can irradiate pipe materials.
Other contaminants such as highly corrosive or explosive contaminants may cause damage to the system
In these cases, systems may choose to replace the contaminated piping and other appurtenances.
9.0 Possible Indicators of a Backflow Incident
This section discusses events, occurrences, or signals that help indicate to a water system or
regulatory authority that a backflow incident is occurring or has occurred. A problem for water systems
in detecting cross-connections is that there is little immediate warning that a backflow incident is
occurring. In some cases it is not known for some time after an incident, and in other cases it is never
discovered. With an active monitoring program, cross-connections may be detected by routine
inspection, and deficiencies in the distribution system that could lead to backflow could be corrected.
However, the efficacy of a cross-connection control program might only be known to the extent that new
backflow incidents are not detected. Possible indicators of backflow include: 1) customer complaints of
water quality; 2) drops in operating pressure; 3) drops in disinfectant residual; 4) water meters running in
reverse; and 5) coliform detections. It is also possible that cross-connections and contamination due to
backflow events can occur in the absence of these indicators.
Customer complaints
From the backflow incident data collected (Exhibit 5.1), the primary indicator of backflow has
been customer complaints of odor, discoloration of the water, or direct physical harm from contact with
the water. Generally, it is unknown how long a backflow incident may have occurred before it is
detected through aesthetic or health concerns.
Drops in operating pressure
Continual monitoring for reduced pressure can give immediate warning of a potential backflow
incident. It may also identify the area where a pressure drop may have originated, and thus help isolate
areas affected by backflow. A drop in operating pressure can only indicate that a backflow event may
have already occurred; it cannot stop an event in progress or prevent an incident, unless the root cause is
corrected.
Drops in Disinfectant Residual
A drop in the disinfectant residual of a distribution system can be an indicator of a backflow
event. Many factors influence the concentration of the disinfectant residual in the distribution system,
including the assimilable organic carbon level, the type and concentration of disinfectant, water
temperature, and system hydraulics (Trussell, 1999). Entry of foreign material into the distribution
system from backflow (or other events) may alter these factors and contribute to a loss of residual.
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Water meters running in reverse
During periods of reversed water flow, water meters can reverse their counters. When
investigating a water quality complaint at a restaurant in Kennewick, WA, a cross-connection specialist
found the meter at the site running backwards; the dual check valves for the carbon dioxide tanks were
impaired, allowing the pressurized carbon dioxide to backflow into the water supply line (AWWA
PNWS, 1995). Based on a survey of water systems, many have the ability to detect meters running
backwards and have detected this occurrence on several occasions (Schwartz, 2002).
Total coliform detections and heterotrophic plate count changes
A sudden spike in total coliform detections, or a sudden change in heterotrophic bacterial
densities (measured by heterotrophic plate count) is an indication that contaminants could have entered
the distribution system (40 CFR 141). Persistent coliform contamination may indicate a long-standing
cross-connection. Monitoring for coliform and other microbial indicators of contamination, as well as
more extensive monitoring, may help identify instances of backflow contamination.
10.0 Research Opportunities
This document identifies what we know regarding the potential health risks associated with
cross-connections and backflow incidents in drinking water distribution systems based on available
literature, research, and information. However, as with most areas, further opportunities exist for
research to result in greater certainty of the health impacts associated with drinking water distribution
systems. Some specific research opportunities, among others, related to cross-connections and backflow
are: further analysis of how surges contribute to occurrence of backflow; the degree of underreporting of
backflow incidents across the country; what constitutes an effective cross-connection control and
backflow prevention program; and what the effectiveness of disinfectant residual is for protecting against
microbial contamination from backflow. It is not feasible to list all specific data needs for cross-
connection control and backflow prevention, but two reports being prepared for EPA as part of its
Comprehensive Drinking Water Research Strategy and the Microbial/Disinfection Byproducts (M/DBP)
Research Council outline additional research opportunities.
11.0 Summary
Cross-connections and backflow represent a significant public health risk (US EPA, 2000b) by
allowing chemical and biological contaminants into the potable water supply (a conclusion of the
Microbial/Disinfection Byproducts Federal Advisory Committee (M/DBP FACA)). Of the 459 backflow
incidents from 1970-2001 on which EPA has information, an estimated 12,093 cases of illness resulted.
Fifty-seven of these cross-connection-related waterborne disease outbreaks were reported to CDC from
1981-1998, and resulted in at least 9,734 cases of illness. A wide number and range of chemical and
biological contaminants have been reported to enter the distribution system through cross-connections
and backflow. Pesticides, sewage, antifreeze, coolants, and detergents were the most frequent types of
contaminants reported. Although a wide range of contaminants have been reported, the number on
contamination incidents is considered a likely underestimate due to problems in detecting, reporting, and
documenting incidents. These problems include: an inability to detect incidents without health effects;
incidents with health effects that are unreported because affected individuals do not realize a connection
between their illness and the drinking water; no requirement on either health officials or water system
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officials to report detected backflow incidents; and no central repository for reported illness. Where
undetected, cross-connections may also expose consumers to contaminants from backflow long-term.
Cross-connections can be prevented through mechanical means and through programs administered by
local or state officials to specifically locate and eliminate cross-connections and prevent backflow.
Officials can also take measures to correct deficiencies that either have the potential to lead to backflow
incidents or have already caused a backflow incident, and they can increase monitoring for indicators of
potential problems to improve reaction time to future incidents.
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