Backflow is the undesired reversal of water flow through a pipe. The normal direction of water flow is from the utility water main (supplier) into homes or businesses (customer). The backflow of water from a consumer’s plumbing system into the public drinking water supply occurs when water flows backward due to a pressure loss in the utility main pipe or increased pressure in the customer’s system due to a pressure source like a well or booster pump.

A backflow prevention device prevents water from flowing back from the customer water system into the Truckee Donner Public Utility District (TDPUD) potable water system. The TDPUD’s Cross-Connection Control Program applies to all types of end-users, including commercial, residential, and industrial customers. The program addresses hazards inherent in uses such as irrigation systems, fire sprinkler systems, boilers, hair salons, medical and dental offices, manufacturing, food service, automotive shops, and pet grooming salons just to name a few.

The two most commonly installed backflow prevention devices are double check valve assemblies (DC) and reduced pressure principle assemblies (RP). TDPUD staff will determine which device is required, depending on the degree of hazard present. These devices must be inspected for proper installation and tested at the time of installation. After the initial test, the device must be tested at least once annually to ensure continued protection against cross-connection. The TDPUD will notify customers of the testing deadline each year. All testing and maintenance shall be performed by a technician with a current backflow prevention assembly tester certification from the American Water Works Association (AWWA) and at the customer’s expense. A list of local AWWA certified testers is available here.  The device shall be protected from freezing.

The required backflow prevention assembly associated with an individual property may be revised by TDPUD staff based upon modifications to the customer’s property and/or the type of business activity. TDPUD staff performs periodic cross-connection control site surveys to identify changes in cross-connection hazards. New commercial and residential establishments are subject to backflow and cross connection review when plans are submitted for construction. Existing establishments are reviewed when a building permit is issued for any alterations. For questions regarding backflow and cross-connection issues, please contact the Water Quality Technician/Inspector at 530-582-3926 or email to waterquality@tdpud.org.

A cross-connection is an actual or potential connection between the public potable water supply and any other system or water source, where it is possible for a contaminant to enter the drinking water supply. The contaminant enters the potable water supply when the pressure of the polluted source exceeds the pressure of the potable water supply. There are two types of backflow: backpressure and backsiphonage.

What is Backsiphonage?

Backsiphonage creates a vacuum as water drains toward the public water system.  Water or fluid can be siphoned or pulled into the utility main water line.

Example: a garden hose with one end immersed in a pail of soapy water or a hose immersed in a swimming pool or sink.

 What is Backpressure?

Backpressure is any elevation of pressure in the downstream (customer) piping system (by pump, elevation of piping, steam pressure, air pressure, etc.) above the distribution supply pressure at the point of consideration, which would cause or tend to cause a reversal of the normal direction of flow.