Frequently Asked Questions
Q. What is
Backflow?
A.
Backflow is the undesirable reversal of flow of
nonpotable water or other substances the 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.
Q.
What is a cross-connection?
A. 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 of system containing nonpotable water or other substances.
Q. What is backsiphonage?
A. Backsiphonage is backflow caused by a negative pressure 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.
Q. What is backpressure
backflow?
A. 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 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.
Q. What is
a backflow preventer?
A. A backflow preventer is a means or mechanism to prevent backflow.
Q. What is
the basic means of preventing backflow?
A. The basic means of preventing backflow is an air gap, which either
eliminates a cross-connection or provides a barrier to backflow.
Q. What is
the basic mechanism for preventing backflow.
A. 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.
Q. Why do
backflow preventers have to be tested periodically?
A. Mechanical backflow preventers have internal seals, springs, and
moving parts that are subject to fouling, wear, or fatigue. Additionally,
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.
Q. Why do
water suppliers need to control cross-connections and protect their public water
systems against backflow?
A. Because backflow into a public water system can pollute or contaminate
the water in that system, making it unusable or unsafe to drink. Each water
supplier has a responsibility to provide water that is usable and safe to drink
under all foreseeable circumstances.