A.  The City of Mesa's water distribution system is designed to keep the water flowing to the customer.  However, when hydraulic conditions within the system deviate from the "normal" conditions, water flow can be reversed.  When this backflow happens, contaminated water can enter the distribution system.

Q.  What causes backflow?

A.  Backflow is possible in two situations, backsiphonage and backpressure.

Q.  What is backsiphonage?

A.  When there is a sudden reduction in the water pressure in the distribution system, such as during firefighting or when a water main breaks, water flow can be reversed.  This can create a suction effect, drawing the non-potable substance into the potable water system.

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Q.  What is backpressure?

A.  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 water system.

Q.  How can backflow be prevented?

A.  Backflow prevention devices:

• Air Gap
• Double Check Valve Assembly
• Reduced Pressure Principal Assembly
• Pressure Vacuum Breaker Assembly

The type of protection required is based on the degree of hazard to the potable water supply.

Q.  What is a backflow assembly?

A.  A backflow prevention devise is an approved, testable assembly which uses valves, in different configurations, to prevent polluted or contaminated water from reversing direction and flowing backward.

Q.  How is an assembly approved?

A.  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 twelve-month field test.  Only assemblies completing the entire testing procedure are recognized by City of Mesa Water as approved backflow prevention assemblies.

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Q.  Who is required to have a backflow prevention assembly?

A.  Federal and State law require that water suppliers protect their water systems from contamination.  State regulations exempt single family residences used solely for residential purposes from assembly requirements.  However, residences used for other purposes, as well as commercial and industrial customers, are required by City Ordinance and State Administrative Code rule R18-4-115 to install and maintain backflow prevention assemblies.

Q.  How do I know if I need a backflow prevention assembly?

A.  A City of Mesa Water Backflow Prevention Inspector will visit your property to do an evaluation for backflow requirements.

Q.  My property is served with reclaimed water.  Do I need backflow protection?

A.  Yes.  Customers receiving reclaimed water must install a Reduced Pressure Assembly (RPA) backflow preventer on all potable water connections, including fire services.

Q.  Who can install a backflow prevention assembly?

A.  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 or replace these assemblies.  Permits are issued by the City of Mesa. 

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Q.  Where should a backflow prevention assembly be located?

A.  Generally, the backflow prevention assembly must be located as close as possible to the water service connection, but must remain on private property.

Q.  Who is responsible for the testing and maintenance of the backflow assembly?

A.  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 will send notices to the customer 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?

A.  The City of Mesa has a list of recognized Assembly Testers that can be provided upon request from the Environmental Division.  Due to the fact that test prices vary among testers, you may want to call several Certified Testers to obtain quotes for your test.