Backflow FAQ

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What is backflow?

The Town of Gilbert water distribution system is designed to keep the water flowing to the customer, however, when hydraulic conditions within the water system deviate from the "normal" conditions, water flow can be reversed. When this backflow happens, contaminated water can enter the distribution system.

What causes backflow?

Backflow is possible in two forms, back-siphonage and backpressure.

What causes back-siphonage?

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

What causes backpressure?

Backpressure is created when pressure in a non-potable system such as in re-circulating pump system, equipment containing soap, acid, or antifreeze, exceeds that in the potable water system that is supplying water to the equipment. Also, landscape reclaim water or untreated water, operating at a higher delivery pressure or (PSI) than the potable water delivery system. This can force the potable water system to reverse its direction of flow through the cross-connection therefore causing non-potable substances to enter the potable water system.

How can backflow be prevented?

By installing backflow prevention assemblies or devices in areas that are rated by degree of hazard or contamination: 

  • Air Gap
  • Atmospheric Vacuum Breakers
  • Pressure Vacuum Breaker Assembly
  • Spill Resistant Vacuum Breaker
  • Double Check Valve Assembly
  • Reduced Pressure Principle Backflow Preventer

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 Town of Gilbert will send notices to customers advising them when an annual test is required on their backflow assembly. The customer must contact a Backflow Assembly Tester, recognized by the Town, 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 report to the Backflow Prevention Department.

How do I find a certified Tester?

The Backflow Prevention Department has a list of recognized Assembly Testers that can be provided upon request. Due to the fact that test prices vary among testers, you may want to call several Certified Assembly Testers to obtain quotes for your test.

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

A Town of Gilbert Backflow Prevention Specialist will visit your property to do an evaluation for any necessary backflow requirements. Call 480-503-6826

How often do I need to have my backflow prevention assembly tested?

Under normal conditions, backflow assemblies need to be tested on an annual basis, but in high hazard conditions, multiple tests may be required each year.

Do I need a permit when installing a backflow prevention assembly?

Yes, a permit is required when replacing an existing backflow assembly that has failed and cannot be repaired. New construction installations do not require a permit.

How much does a Backflow Installation permit cost?


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

Yes. Customers receiving reclaimed water must install a Reduced Pressure Backflow Preventer on all potable water (meters) connections to standard detail including fire services.