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.
(TOP)
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. (TOP)
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. (TOP)
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. (TOP)
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. (TOP)
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. Alteratively, 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: (I ) 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
(S) 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. (TOP)
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.
(TOP)
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. (TOP)
QUESTION: What is a reduced 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. (TOP)
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 eqipped with test
cocks. A PVB may be used to isolate health or nonhealth hazards but is effective
against backsiphonage only. (TOP)
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. (TOP)
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. (TOP)
QUESTION: Where can I get more information about cross-connection control?
ANSWER: One 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; 213/740-2032; http://www.usc.edu/dept/fccchr.
Another 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; 800/926-7337;
http://www.awwa.org. (TOP)