Backflow Prevention

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What is backflow? Backflow

The water distribution system is designed to keep water flowing to the customer - evenly and consistently. Sometimes the normal flow is reversed by backsiphonage or backpressure. Backflow is the undesirable reversal of flow which could allow water that has gone through a customer's water meter back into the distribution system. When this reversal of flow happens, contaminated water can enter the distribution system through a cross-connection.

What is a cross-connection? 

A cross-connection occurs when there is a connection between potable (safe to drink) water and non-potable water supplies. The City of Mesa has a cross-connection control program (backflow prevention program) as required by state code to protect the drinking water supply from contamination caused by backflow.

How does this affect me as a residential customer?

Be aware of cross-connections or backflow hazards and where they might occur. 

Potential residential cross-connections: 

  • Garden hoses attached to the water supply that are placed in buckets of standing water or chemicals, or in swimming pools, pet watering bowls, or garden sprayers.
  • Faucets not high enough to avoid contact with standing water or chemicals.  
  • Improper height of the overflow tube in the toilet tank, which could allow the fill valve to become submerged.  
  • Landscape watering systems that inter-connect City water with an irrigation water supply.
  • Unprotected landscape watering systems that can allow water and chemicals to be drawn back into the home if a drop in water pressure occurs.

Avoid creating the potential for a cross-connection or backflow. Properly installed and maintained backflow prevention assemblies are critical to maintaining safe drinking water supplies. Backflow prevention assemblies should be tested for proper operation on an annual basis. If the assembly needs repair, have a qualified professional repair it immediately. An assembly that is not functioning properly can be just as hazardous as not having one at all.

A qualified plumber or backflow prevention assembly tester can determine if the assembly is functioning properly. Make sure their certifications and licenses are valid and current and that the individuals are recognized as "qualified and accepted" by the City of Mesa.

When installing a backflow prevention assembly or other piece of equipment that requires a direct connection to the potable water supply, obtain a permit from the City to ensure you meet the minimum backflow requirements. Not all backflow prevention assemblies meet minimum requirements.


How does this affect me as a commercial customer?

Obtain a permit through the Department of Development & Sustainability (480-644-4273) prior to installing backflow protection in a commercial or industrial setting. The Water Quality Services office maintains a list of premises requiring backflow prevention assemblies.

Potential cross-connections in public places: 

  • Fountains, including drinking fountains (if the water nozzle or supply is below the flood rim of the fountain.)
  • Hoses attached to the potable water supply faucets and extended into sinks, buckets, drains, chemical mixing containers, etc. 
  • Hoses should not be submerged in swimming pools or hot tubs. 
  • Faucets should be high enough to never come in contact with standing water, chemicals, etc.

For more information see below and also visit our Backflow FAQ Page.


Robert Judd, Water Quality, 480-644-2885,

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