Requirements & Types of Backflow Prevention

Seattle Public Utilities requires that any actual or potential cross-connection be either eliminated or be properly protected. Backflow prevention may be required to be installed by the customer on the water service line outside the building, at one or more location within the building, or both. After the initial installation and testing of a new backflow preventer, the customer is required to have the backflow preventer tested on an annual basis to help ensure it is working to keep both the customer's water and the City of Seattle's water safe from contamination.

Backflow prevention is also required by the Uniform Plumbing Code (UPC). Within Seattle's city limits, Public Health - Seattle & King County (PH-S&KC) is the plumbing authority. Within Shoreline's city limits, the City of Shoreline is the plumbing authority. Seattle Public Utilities works with both PH-S&KC and the City of Shoreline when it comes to backflow prevention requirements and helping to keep the city's drinking water safe from potentially harmful backflows and contamination.

Types of backflow prevention that may be required/approved:

  • Air gaps (AG)
  • Reduced Pressure Backflow Assemblies (RPBA) / Reduced Pressure Detector Assemblies (RPDA)
  • Double Check Valve Assemblies (DCVA) / Double Check Detector Assemblies (DCDA)
  • Spill-resistant Vacuum Breakers (SVBA)
  • Pressure Vacuum Breaker Assemblies (PVBA)


Required Backflow Prevention

The backflow prevention required is determined by the hazard. Seattle Public Utilities' certified Cross-connection Control Specialists make the determination of what type of protection is required for each specific installation. Below are the general guidelines.

High hazards: High Health Hazard facilities are required to have Premises Isolation, which is an approved backflow assembly installed just downstream of the water meter/city union, where the transfer of ownership happens. Seattle Public Utilities requires a Reduced Pressure Backflow Assembly (RPBA/RPDA) as Premises Isolation for high health hazards.

Examples of high health hazard facilities that may be found in Seattle include but are not limited to:

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

Low hazards: Seattle Public Utilities accepts Double Check Valve Assemblies (DCVA/DCDA), Spill-resistant Vacuum Breaker Assemblies (SVBA), and Pressure Vacuum Breaker Assemblies (PVBA) as types of protection for low hazards. Examples of low hazards are irrigation systems, fire systems, and buildings exceeding 3 stories or 30' in height.

Approved backflow prevention assembly: The backflow assembly installed must be approved for use in Washington State. The list can be found at USC Foundation ( Any backflow assemblies not currently listed must have been listed at the time of original installation.


Inspection and Annual Testing

Seattle Public Utilities (SPU) requires that all backflow assemblies be inspected upon installation and may require periodic re-inspection of existing assemblies. New assemblies must be installed in an approved manner and be tested by a State of Washington certified Backflow Assembly Tester (BAT) prior to being put into service. The customer must ensure that a copy of these initial test reports are provided to SPU or the plumbing authority performing the inspection.

All installed backflow assemblies must then be tested annually by a State of Washington certified backflow assembly tester, as well as after any repair or replacement. A copy of the test report must be provided directly to SPU.


Contact Us

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


Public Utilities

Andrew Lee, General Manager and CEO
Address: 700 5th Avenue, Suite 4900, Seattle, WA, 98104
Mailing Address: PO Box 34018, Seattle, WA, 98124-5177
Phone: (206) 684-3000

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Seattle Public Utilities (SPU) is comprised of three major direct-service providing utilities: the Water Utility, the Drainage and Wastewater Utility, and the Solid Waste Utility.