What is Backflow?

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.

What is a Backflow Prevention Device?

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

What is Cross-Connection?

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.

Are there District Policies regarding backflow?




6.56.010 Purpose 
6.56.020 District Responsibilities 
6.56.030 Customer Responsibilities 
6.56.040 Protective Devices Required 
6.56.050 Testing and Maintenance 
6.56.060 Fees and Charges

 6.56.010 Purpose The purpose of this policy is to:

1. Protect the District’s potable water supply from the possibility of contamination or pollution by isolating within the customer's internal distribution system(s) or the customer's private water system(s) any contaminants or pollutants which could backflow into the public water systems. 

2. Promote the elimination or control of existing cross-connections, actual or potential, between the customer's in-plant potable water system and non-potable water system, plumbing fixtures and industrial piping systems. 

3. Provide for the maintenance of a continuing program of cross-connection control which will systematically and effectively prevent the contamination or pollution of all potable water systems. 

4. The District shall have a backflow prevention and cross-connection control program which meets or exceeds all State and Federal rules and regulations.

 6.56.020 District Responsibilities The District shall be responsible for the protection of the public potable water distribution system from contamination or pollution due to the backflow of contaminants or pollutants through the water service connection. It is the responsibility of the District to evaluate the hazards beyond the service connection in a customer's water system to determine whether pollutants or contaminants are, or may be, handled on the customer's premises in such a manner as to possibly permit contamination of the public water system. The District has the right to disconnect service to any customer whose water system may potentially harm the public water system. 

When a hazard or potential hazard to the public water system is found or suspected, the customer shall be required to install an approved backflow prevention assembly at each public water service connection to the premises in accordance with District rules and regulations. The District shall not be responsible for any loss or damage directly or indirectly resulting from or caused by the proper, improper or negligent installation, operations, use, repair or maintenance of, or interfering with, any protective device by any customer or any other person. 

6.56.030 Customer Responsibilities The customer shall be required to furnish and install, in a manner approved by the District, and keep in good working order and safe condition, any and all backflow prevention assemblies. All backflow prevention assemblies shall be owned and maintained by the customer. All backflow prevention assemblies shall be tested at the time of installation and annually thereafter. In the event of high hazard installations, the District may require more frequent testing. Backflow prevention assemblies shall be tested by a certified backflow prevention assembly tester and test reports shall be submitted to the District. In the event that a backflow prevention assembly is found to be damaged, defective or operating improperly, it shall be repaired or replaced by the customer. The customer shall not bypass or render inoperative any backflow prevention assembly. If a backflow prevention assembly is temporarily removed for repair or other reason, the customer shall provide an approved backflow prevention assembly, tested by a certified backflow prevention assembly tester at the time of installation. The customer is to maintain an adequate heat source to any backflow prevention assembly housings in order to prevent cold weather from affecting the operation of the assembly. Once notified of the need to install a backflow prevention assembly, the customer shall immediately install such approved assembly at the customer's own expense. Failure, refusal or inability on the part of the customer to install, have tested and maintain said assembly shall constitute sufficient grounds for disconnection of water service to the premises until such requirements have been satisfactorily met. 

6.56.040 Protective Devices Required The protection required to prevent backflow into the public water system shall be commensurate with the degree of hazard that exists on the customer's premises. The District shall determine the type of backflow prevention assembly. 

6.56.050 Testing and Maintenance All backflow prevention assemblies shall be tested annually to assure proper operation. In instances where a hazard is deemed great enough, testing may be required at more frequent intervals. Such intervals shall be determined by the District. The customer shall bear all costs of device testing. The cost of any maintenance required as a result of inspections or testing is the responsibility of the customer. Maintenance work shall be performed by private contract. Records of inspections, testing or repairs shall be kept by the District and made available to the appropriate regulatory agencies. 

The District shall notify the customer when tests are required and supply the necessary test forms and instructions. These forms will be completed by the certified backflow-prevention tester and returned to the District by the date indicated. 

If a device is found to be in non-compliance by inspection and/or testing, the customer shall be notified in writing. The customer shall correct any deficiency within 15 calendar days of notification, at which time the inspection shall be repeated. The District shall disconnect water service if a backflow prevention device has failed to be tested properly or properly maintained or installed. Notification of intent to terminate water service shall be commensurate with the hazard to public health and may be delivered to the tenant, owner, or both as the situation requires. 

6.56.060 Fees and Charges Backflow prevention devices shall be subject to fees and charges to allow the District to recover the costs of administering the backflow prevention program. Such fees and charges shall be posted in a schedule approved by the District’s Board of Directors.