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Requirements & Types of Devices

Seattle Public Utilities requires that any cross connection have a backflow preventer. The backflow preventer may be required to be located on the water service line, within the building, or both locations. After an initial inspection and testing of a newly installed backflow preventer, the water customer is required to have the backflow preventer tested on an annual basis.

Backflow preventers are also required by the plumbing code. Except within Shoreline, the plumbing authority for Seattle Public Utilities customers is King County plumbing (Public Health – Seattle & King County). The City of Shoreline is the plumbing authority within Shoreline’s city limits. Seattle Public Utilities works with both King County plumbing and the City of Shoreline when it comes to backflow preventer requirements.

Several types of backflow preventers are available:

  • Air gaps (AG)
  • Reduced pressure backflow assemblies (RPBA)
  • Double check valve assemblies (DCVA)
  • Pressure vacuum breaker assemblies (PVB)
  • Atmospheric vacuum breakers (AVB)

What type do I need?

The assembly you need is determined by the hazard. Seattle Public Utilities’ staff makes the determination of what type of device is acceptable for each specific installation. Here are the general guidelines:

High hazards: Seattle Public Utilities accepts air gaps and reduced pressure backflow assemblies as protection for different types of high hazards. Examples of high hazard facilities:

  • Beverage bottling plants
  • Car washes
  • Chemical plants
  • Commercial laundries and dry cleaners
  • Premises where both reclaimed water and potable water are provided
  • Film processing facilities
  • Food processing plants
  • Hospitals, medical centers, nursing homes, veterinary, medical and dental clinics, and blood plasma centers 
  • Premises with separate irrigation systems using the purveyor's water supply with chemical addition
  • Laboratories
  • Metal plating industries
  • Mortuaries
  • Petroleum processing or storage plants
  • Piers and docks
  • Wastewater lift stations and pumping stations
  • Wastewater treatment plants

Low hazards: Seattle Public Utilities accepts double check valve assemblies, pressure vacuum breaker assemblies and atmospheric vacuum breakers as types of protection for low hazards. Examples of low hazards are fire systems and irrigation systems.

Use an approved device: The backflow preventer you choose must be listed on the Washington State Department of Health's Approved Backflow Prevention Assembly List. Assemblies not currently listed must have been listed at the time of original installation.

Inspection of backflow preventers

Seattle Public Utilities inspects backflow assemblies upon installation and conducts periodic re-inspections on all existing assemblies. New assemblies must be tested by a State of Washington certified backflow assembly tester prior to putting into service. A copy of the test report must be provided to us.

Annual testing of backflow preventers

All backflow preventers must be tested annually by a State of Washington certified backflow assembly tester and after repair or replacement. A copy of the test report must be provided to us.

Contact us

For answers to specific cross-connection control questions, lists of approved assemblies or certified testers, or to request an inspection, call (206) 684-3536.