Backflow prevention and cross-connection

	Video
	Learn how backflow prevention devices protect our water supply. (4:16)

The Water District works with its customers to protect the drinking water supply from pollution and contamination caused by cross-connections and backflow.

Backflow occurs when water that has already entered a facility flows back into the public water system.

A cross-connection is a point in a plumbing system where the potable (drinking) water supply is or can be directly connected to a nonpotable source (water unfit for drinking).

What causes water to flow backward?

There are two causes for water to flow back into the public water supply: backsiphonage and back pressure.

Backsiphonage is the reverse flow of water due to negative pressure. Backsiphonage is created when water mains experience a sudden drop in water pressure due to water main breaks or nearby firefighting efforts.

Back pressure occurs when heating systems, elevated tanks and pressure-producing systems create pressure in your plumbing that exceeds the water system pressure.

How do you prevent backflow?

A backflow prevention assembly is a testable, mechanical device that uses check valves to prevent polluted or contaminated water from flowing backwards. Some assemblies eliminate backflow by discharging used water to the ground. Assemblies installed as a secondary protection should be located as close as possible to the water meter.

Does every water customer need to install an assembly?

State regulations currently exempt single-family homes used solely for residential purposes from assembly requirements. Other facilities may need to be inspected to determine the type of water use and whether an assembly is required.

The Water District has a comprehensive backflow prevention program which includes the installation of backflow prevention assemblies on all commercial, multifamily, residential and irrigation services.

Can check valves be used as a backflow prevention assembly?

A check valve is not equipped with test connections to assure that the valve is preventing backflow. That’s why only approved assemblies are allowed.

What is an approved assembly?

An approved assembly is any type of backflow prevention assembly that has been tested and approved by an independent testing laboratory and the Water District.

If my building was recently modified to meet city code requirements by installing backflow assemblies internally, do I still need them at the service connection?

Even though plumbing code provisions may be rigidly enforced on new installations, experience has shown that “on-site” modifications and alterations of private plumbing are common. Possible hazards to the public water supply can be created due to backflow from private plumbing. These hazards may be caused by a submerged hose or complex mechanical failure. In most cases the only practical way to assure protection is to install a backflow assembly at the point of service delivery. That way, regardless of what happens inside the customer’s property or what changes are made to private plumbing, the public water supply is protected.

Where do I get a permit to install a backflow prevention assembly?

The customer works directly with the Water District to get the process started. Backflow assemblies are installed according to Water District installation requirements. The final installation is inspected by the Water District.

For more information, call our Water Quality Division at (702) 258-3215 and ask to speak to the backflow supervisor or contact us.