back-flow Prevention

Frequently Asked Questions

Q. What is back-flow?

A. The water distribution system is designed to keep the water flowing from the distribution system to you the customer. However, when hydraulic conditions within the system deviate from the "normal" conditions, water flow can be reversed. When this back-flow happens, contaminated water can enter the distribution system.

Q. What causes back-flow?

A. back-flow is possible in two situations, backsiphonage and back-pressure.

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.

Q. What is back-pressure?

A. Back-pressure is created when pressure in a non-potable system, such as in a recirculating system containing soap, acid, or antifreeze, exceeds that in the potable system that provides make up 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 back-flow be prevented?

A. Tempe recognizes four methods of back-flow prevention:

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

The Environmental Division will determine which type of protection is required based on the degree of hazard that the property represents to the potable water supply.

Q. What is a back-flow assembly?

A. A back-flow preventer 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 back-flow 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 laboraton/tests and a twelve month field test. Only assemblies completing the entire testing procedure are recognized by Tempe Water as approved back-flow prevention assemblies.

Q. Who is required to have a back-flow 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, may be required to install and maintain back-flow prevention assemblies. When a determination is made by health official that the potable water system may be subject to contamination through back-flow, a back-flow prevention assembly will be required. Tempe Environmental Division makes these decisions on a case by case basis.

Q. My property is served with reclaimed water. Do I need back-flow protection?

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

Q. Who can install a back-flow prevention assembly?

A. The installation of the back-flow prevention assembly should only be done by a licensed professional.

Q. Where should a back-flow prevention assembly be located?

A. Generally, the back-flow prevention assembly must be located as close as possible to the water service connection, but must remain on private property. Contact a licensed professional for information on variances.

Q. Who is responsible for the testing and maintenance of the back-flow assembly?

A. It is the sole responsibility of the customer to ensure that the assembly is in satisfactory operating condition at all times. Annual testing is required to stay in compliance. The customer must contact a recognized or licensed back-flow 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 back-flow Prevention Section.