Q. What is backflow?
The City of Mesa's water distribution system is designed to
keep the water flowing to the customer. However, when hydraulic
conditions within the water distribution system deviate from "normal"
flow patterns, water flow to the customer can be reversed. When this
undesirable reversal of flow
happens, contaminated water can enter the distribution system
through a cross-connection.
Q. What is a cross-connection?
A cross-connection is an actual or potential connection between
potable* water plumbing to a non-potable pipe system, to water
that has been discharged from the potable water plumbing not
separated by an air gap, or any fluid or substance that
originated from outside the potable water plumbing.
Q. What are some examples of cross-connections?
A swimming pool auto fill line
A landscape sprinkler or drip system
A decorative fountain that has an auto fill line
A hose bib or any outlet that will accommodate the attachment of
Most fire sprinkler systems
Plumbing connected equipment or apparatus
Q. What causes backflow?
Backflow is caused by the presence of an unprotected
cross-connection to the public water supply or a customer's
potable water plumbing during a back-siphon or backpressure
Q. What is back-siphonage?
Back-siphonage is a sudden reduction in the water
pressure in the distribution system, such as during firefighting
activities, or when a water main breaks, vigorous water main
flushing events, electric power interruption, or distribution
system equipment failure. These events may drastically lower
distribution system pressure and create a suction effect. This
can draw a non-potable substance or water that has been
contaminated by contact with the environment into the potable
water system through a cross connection.
Q. What is backpressure?
Backpressure is created when pressure in a non-potable
system, such as in a re-circulating system containing soap,
acid, or antifreeze, exceeds that in the potable system that
provides makeup water to the system. This can force the potable
water to reverse its direction of flow through the cross
connection. Non-potable substances can then enter the potable
Q. How can backflow be prevented?
Backflow can be prevented by the installation of backflow prevention
assemblies, methods, or devices, such as: Air Gap (AG); Double Check Valve
Assembly (DC); Reduced Pressure Principal Assembly (RP); Pressure Vacuum
Breaker Assembly (PVB); and Spill Resistant Pressure Vacuum
Breaker (SVB). A backflow prevention assembly is effective
in the prevention of backflow only if installation criteria are
strictly followed. The type of assembly needed is based on the
degree of hazard to the potable water supply.
Q. What is a backflow assembly?
A backflow assembly is an approved, testable
assembly which uses valves, in different configurations, to
prevent polluted or contaminated water from reversing direction
and flowing backward into a customer's potable water plumbing or
in the municipal water distribution system.
Q. How is an assembly approved?
An approved backflow prevention assembly has gone through an
approval process at the
Foundation for Hydraulic Research and Cross Connection Control
at the University of Southern California. This is a
two-step process consisting of laboratory tests and a
12-month field test. Only assemblies completing the entire
testing procedure are recognized by the City of Mesa Water
Resources Department as
approved backflow prevention assemblies.
Q. Who is required to have a backflow prevention
Any water customer with a cross-connection is required to
install appropriate backflow protection.
Federal and State laws require that water suppliers protect
their water systems from contamination by requiring the
installation and testing of appropriate backflow assemblies. Commercial and industrial
customers and homes with dedicated landscape meters are
required by City Ordinance and State
Administrative Code rule R18-4-215 to install, test, and maintain
backflow prevention assemblies. In addition, the City of Mesa
has adopted the 2006 International Plumbing Code. This code
specifies backflow requirements for water customers including
all single family residences.
Q. How do I know if I need a backflow prevention
If you maintain a cross-connection on your property,
you must protect your family and neighbors, as well as other
water customers, from a
backflow event by isolating the cross-connection as required by
code with a properly installed backflow assembly. Additional
guidance to this end is provided on this website. Specific
questions or concerns can be addressed by calling our Backflow
Prevention/Cross Connection Control Mailbox at (480) 644-6462.
Q. I have access to auxiliary** water on my
property. Do I
need backflow protection?
Yes. Customers receiving auxiliary water must install a
Reduced Pressure Assembly (RPA) backflow preventer on all
potable water connections, including fire services.
(See explanation below for clarification of "auxiliary" water.)
Q. Who can install a backflow prevention assembly?
The installation of the backflow prevention assembly is the
responsibility of the customer. The assembly may be installed
by a property owner, plumbing contractor, or a general
contractor, subject to the Rules and Statutes of the Arizona
Registrar of Contractors. Permits are required to install these assemblies. Permits are issued by the City of
Q. Where should a backflow prevention assembly be
Generally, the backflow prevention assembly must be located
as close as possible to the water service connection, but must
remain on private property. Individual cross-connections must be
isolated with a properly installed backflow assembly at the
connection point to the potable water supply.
Q. Who is responsible for the testing and
maintenance of the backflow assembly?
It is the sole responsibility of the customer to ensure that the
assembly is in satisfactory operating condition at all times.
The City of Mesa Water Resources Department will send notices to regulated customers
advising them when an annual test is required on their backflow
assembly. The customer must contact a recognized Backflow
Assembly Tester to perform the test. If any repair work or
maintenance is performed on the assembly, a recognized Tester
must retest the assembly immediately and submit the test results
to the City of Mesa.
Q. How do I find an approved Certified Tester?
The City of Mesa maintains a list of
approved Backflow Assembly Testers. Due to the fact that prices vary among testers,
you may want to call several Certified Testers to obtain quotes
for your test.
Tester Application Form
*Potable: Water from any source which has been investigated
by the health agency having jurisdiction, and which has been
approved for human consumption.
**Auxiliary Water: Water not under the sanitary control of
the City of Mesa Water Resources Department. For our definition,
this will include: reclaimed water (treated wastewater); well
water; impoundments containing raw, municipal or any other
water; municipal water from another purveyor; grey water; or
recycled rain water.