Backflow Requirements

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Backflow is the undesired reverse flow of liquids in a water service line, such as flow from an irrigation line into a building’s domestic drinking water line. Two situations can cause backflow:

The District requires the use of backflow prevention devices at certain types of facilities to prevent contamination of the water supply.

Approved Backflow Prevention Devices And Testers

The District refers to the List of Approved Backflow Prevention Assemblies maintained by the University of Southern California Foundation for Cross-Connection Control and Hydraulic Research.  The list can be obtained online from the USC Foundation.

The District maintains a list of approved backflow testers who are certified by an approved program. To become an approved tester, see Backflow Device Testing.
Reduced Principal Assembly
Double Detector Check Assembly

Types Of Backflow Devices

Reduced Pressure Principal Assemblies for Domestic Service Lines

A reduced pressure principal (RP) assembly offers sophisticated protection against back siphonage and back pressure in domestic water service lines. The RP device has a relief valve located between two check valves. The relief valve will discharge water should either check valve fail. The RP device requires annual testing.

Installation requirements:

  • Install horizontally, a minimum of 12 inches and no more than 36 inches above finished grade.
  • Must have adequate clearance on all sides for testing and maintenance.
  • Requires testing when installed and annually thereafter.

Double Detector Check Assemblies for Fire Service Lines 

A double check-detector backflow prevention assembly (DCDA) is used on main fire service lines. A DCDA consists of two backflow devices, one on the main line and the other on a bypass line. The bypass line device contains a small meter for detecting water use.

A DCDA lacks a relief valve and thus does not provide the highest level of protection. If chemicals are added to an onsite fire-fighting system, a reduced pressure principal detector check assembly (RPDA) must be installed to provide additional protection. 

All fire service backflow devices are required to be tested annually to ensure proper working order.

Fire Service Line Meters

Fire service lines must have a meter installed on the DCDA or RPDA assembly. The meters must be inspected regularly to ensure proper working order. When a non-working meter is replaced, use a meter reading form to document the old meter’s last reading and number and the new meter’s number, last reading, and new reading.


Commercial, Industrial, Irrigation, and Multi-family Customers

The California Code of Regulations, Title 17, specifies where backflow prevention devices must be installed to protect the public drinking water systems from contamination. Generally these devices are installed at industrial, commercial, and institutional facilities like hospitals, restaurants, public parks, and auto shops; and at multi-family facilities. Backflow prevention devices also are required on the potable water systems at facilities that use recycled water for irrigation or other nonpotable uses.

The District requires that commercial, industrial, irrigation, and multi-family facilities install RP devices on their potable water service lines. Fire service lines, at a minimum, must have a DCDA installed. If chemicals are added to the fire system, an RPDA must be installed.

Residential Customers
Typically, residential customers are not required to install backflow protection devices on incoming water service lines. However, if any of the devices listed below is connected to a residential plumbing system, a backflow protection device must be installed on the incoming water service line as close as possible to the water meter.
  • Sewer ejector pump
  • Rainwater collection system
  • Graywater system
  • Groundwater well
  • Recycled water system
  • Septic system
  • Other auxiliary water systemhose bib vacuum breaker

The District recommends that homeowners install hose bib vacuum breakers on all hose bibs.Homeowners occasionally install washing or chemical feeding equipment (such as a plant fertilizer sprayer) on hose bibs. This equipment can create backflow that could contaminate both the home’s water supply and the public supply. Installing hose bib vacuum breakers on all hose bibs is an easy and inexpensive way to prevent harmful contamination.

Lead-Free Plumbing

Since January 1, 2010, California law has required that only lead-free pipes, plumbing fittings, or fixtures be used for the installation or repair of any public water system or any plumbing in a facility providing water for human consumption. In conformance with this law, the District requires lead-free devices for all new or replacement backflow preventers installed on potable services used for human consumption. If an existing device fails backflow testing and requires repairs, and the device contains lead, the existing device must be replaced with an approved lead-free device.

Backflow Fee

DSRSD charges a bimonthly administration fee to customers that are required to install backflow prevention devices. This fee funds the District’s efforts to comply with the Department of Public Health’s requirements to protect the public water system from backflow contaminants. The District’s Backflow/Cross Connection Prevention Program ensures that backflow devices on irrigation, fire, and drinking water systems in commercial and industrial buildings are tested and in good working order. The District complies with all Department of Public Health regulations and submits required reports.

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