Cross
Connection Control and Backflow Prevention Program
QUESTION: What is a
cross-connection?
ANSWER: A cross-connection is any temporary or
permanent connection between a public water system or
consumer’s potable (i.e., drinking) water system and
any source or system containing nonpotable water or other
substances. An example is the piping between a public
water system or consumer’s potable water system and an
auxiliary water system, cooling system, or irrigation
system.
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QUESTION:
What is backflow?
ANSWER: Backflow is the undesirable reversal of flow
of nonpotable water or other substances through a
cross-connection and into the piping of a public water
system or consumer’s potable water system. There are
two types of backflow--backpressure backflow and backsiphonage.
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QUESTION:
What is backpressure backflow?
ANSWER: Backpressure backflow is backflow caused by a
downstream pressure that is greater than the upstream or
supply pressure in a public water system or consumer’s
potable water system. Backpressure (i.e., downstream
pressure that is greater than the potable water supply
pressure) can result from an increase in downstream
pressure, a reduction in the potable water supply
pressure, or a combination of both. Increases in
downstream pressure can be created by pumps, temperature
increases in boilers, etc. Reductions in potable water
supply pressure occur whenever the amount of water being
used exceeds the amount of water being supplied, such as
during water line flushing, fire fighting, or breaks in
water mains.
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QUESTION:
What is backsiphonage?
ANSWER: Backsiphonage is backflow caused by a
negative pressure (i.e., a vacuum or partial vacuum) in a
public water system or consumer’s potable water system.
The effect is similar to drinking water through a straw.
Backsiphonage can occur when there is a stoppage of water
supply due to nearby fire fighting, a break in a water
main, etc.
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QUESTION:
Why do water suppliers need to control cross-connections
and protect their public water systems against backflow?
ANSWER: Backflow into a public water system can
pollute or contaminate the water in that system (i.e.,
backflow into a public water system can make the water in
that system unusable or unsafe to drink), and each water
supplier has a responsibility to provide water that is
usable and safe to drink under all foreseeable
circumstances. Furthermore, consumers generally have
absolute faith that water delivered to them through a
public water system is always safe to drink. For these
reasons, each water supplier must take reasonable
precautions to protect its public water system against
backflow.
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QUESTION:
What should water suppliers do to control
cross-connections and protect their public water systems
against backflow?
ANSWER: Water suppliers usually do not have the
authority or capability to repeatedly inspect every
consumer’s premises for cross-connections and backflow
protection. Alternatively, each water supplier should
ensure that a proper backflow preventer is installed and
maintained at the water service connection to each system
or premises that poses a significant hazard to the public
water system. Generally, this would include the water
service connection to each dedicated fire protection
system or irrigation piping system and the water service
connection to each of the following types of premises:
(1) premises with an auxiliary or reclaimed water system;
(2) industrial, medical, laboratory, marine or other
facilities where objectionable substances are handled in
a way that could cause pollution or contamination of the
public water system; (3) premises exempt from the State
Plumbing Code and premises where an internal backflow
preventer required under the State Plumbing Code is not
properly installed or maintained; (4) classified or
restricted facilities; and (5) tall buildings. Each water
supplier should also ensure that a proper backflow
preventer is installed and maintained at each water
loading station owned or operated by the water supplier.
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QUESTION:
What is a backflow preventer?
ANSWER: A backflow preventer is a means or mechanism
to prevent backflow. The basic means of preventing
backflow is an air gap, which either eliminates a
cross-connection or provides a barrier to backflow. The
basic mechanism for preventing backflow is a mechanical
backflow preventer, which provides a physical barrier to
backflow. The principal types of mechanical backflow
preventer are the reduced-pressure principle assembly,
the pressure vacuum breaker assembly, and the double
check valve assembly. A secondary type of mechanical
backflow preventer is the residential dual check valve.
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QUESTION:
What is an air gap?
ANSWER: An air gap is a vertical, physical separation
between the end of a water supply outlet and the
flood-level rim of a receiving vessel. This separation
must be at least twice the diameter of the water supply
outlet and never less than one inch. An air gap is
considered the maximum protection available against
backpressure backflow or backsiphonage but is not always
practical and can easily be bypassed.
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QUESTION:
What is a reduced-pressure principle assembly (RP)?
ANSWER: An RP is a mechanical backflow preventer that
consists of two independently acting, spring-loaded check
valves with a hydraulically operating, mechanically
independent, spring-loaded pressure differential relief
valve between the check valves and below the first check
valve. It includes shutoff valves at each end of the
assembly and is equipped with test cocks. An RP is
effective against backpressure backflow and backsiphonage
and may be used to isolate health or nonhealth hazards.
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QUESTION:
What is a pressure vacuum breaker assembly (PVB)?
ANSWER: A PVB is a mechanical backflow preventer that
consists of an independently acting, spring-loaded check
valve and an independently acting, spring-loaded air
inlet valve on the discharge side of the check valve. It
includes shutoff valves at each end of the assembly and
is equipped with test cocks. A PVB may be used to isolate
health or nonhealth hazards but is effective against
backsiphonage only.
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QUESTION:
What is a double check valve assembly (DC)?
ANSWER: A DC is a mechanical backflow preventer that
consists of two independently acting, spring-loaded check
valves. It includes shutoff valves at each end of the
assembly and is equipped with test cocks. A DC is
effective against backpressure backflow and backsiphonage
but should be used to isolate only nonhealth hazards.
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QUESTION:
What is a residential dual check valve (rdc)?
ANSWER: An rdc is similar to a DC in that it is a
mechanical backflow preventer consisting of two
independently acting, spring-loaded check valves.
However, it usually does not include shutoff valves, may
or may not be equipped with test cocks or ports, and is
generally less reliable than a DC. An rdc is effective
against backpressure backflow and backsiphonage but
should be used to isolate only nonhealth hazards and is
intended for use only in water service connections to
single-family homes.
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QUESTION:
Why do backflow preventers have to be tested
periodically?
ANSWER: Mechanical backflow preventers have internal
seals, springs, and moving parts that are subject to
fouling, wear, or fatigue. Also, mechanical backflow
preventers and air gaps can be bypassed. Therefore, all
backflow preventers have to be tested periodically to
ensure that they are functioning properly. A visual check
of air gaps is sufficient, but mechanical backflow
preventers have to be tested with properly calibrated
gauge equipment.
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QUESTION:
Where can I get more information about cross-connection
control and backflow prevention?
ANSWER:
- The
University of Florida TREEO Center maintains a
Backflow
Prevention and Cross-Connection Control Program Page.
In addition to information about training and
recertification, you can also find useful information
about backflow case histories, find assistance for a
cross-connection control program, contact information
for organizations involved in water quality, and
more.
- One
excellent reference manual is the second (1990)
edition of the American Water Works Association’s (AWWA’s) Manual M14, Recommended Practice for
Backflow Prevention and Cross-Connection Control,
which is available from the
AWWA
Bookstore; 6666 West Quincy Avenue; Denver,
Colorado 80235; telephone 800-926-7337.
- Another
excellent reference manual is the ninth (1993)
edition of the University of Southern California’s
Manual of Cross-Connection Control, which is
available from the
Foundation
for Cross-Connection Control and Hydraulic Research;
University of Southern California; KAP-200 University
Park MC-2531; Los Angeles, California 90089-2531;
telephone 213-740-2032.
2012 State of Florida