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Backflow Assembly Requirements

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This information should not be used as the sole basis for the design and installation of backflow prevention assemblies. These are general requirements and do not include jurisdiction specific requirements. Please contact Tacoma Water Quality at (253) 502-8215 for specific requirements.

Assembly Requirements

1. All assemblies must be listed on the current State of Washington - Department of Health Approved Backflow Prevention Assemblies List. If not currently listed, they must have been listed at the time of original installation.

2. All assemblies must be inspected by Tacoma Water upon installation or replacement and periodically thereafter. Tacoma Water will tag inspected and approved assemblies. Customers may request inspections online, or at (253) 502-8215 or We do our best to accommodate inspections within one business day.

3. All assemblies are required to be tested by a State of Washington Certified Backflow Assembly Tester upon installation, repair or replacement and annually thereafter.

4. All assemblies must be installed in the physical orientation for which they were approved.

5. Assemblies two and a half inches and larger must be supported to prevent damage.

6. Assemblies shall not be installed in a location where spillage or relief valve operation will present a hazardous condition. Example: adjacent to electrical switchgear/panels.

7. For assemblies installed below ground:
  • In an irrigation box, the top of assembly can be no deeper than 12 inches from the finished elevation.

  • Assemblies less than two and a half inches must have a minimum 6-inch clearance under the assembly.

  • Assemblies two and a half inches and larger must have a minimum one-foot clearance under assembly.

  • Assemblies installed in vaults must have a permanently installed ladder to allow safe access.

  • Plugs must be installed in each of the test cocks. Plugs must fit snugly.

  • Provisions for water drainage must be provided.

All assembly bypasses must have backflow protection equivalent to the assembly being bypassed.

9. All above ground assemblies must be installed between one and five feet above the finished floor elevation, unless a permanent platform is installed to facilitate testing and maintenance.

10. No assembly shall be installed in an environment containing toxic, corrosive or hazardous fumes.

11. Assemblies shall not be installed in crawl spaces or attics.

12. Assemblies shall be located such that they are protected from accidental damage.

13. Specific requirements for landscape irrigation systems can be found in Tacoma Water's Guidelines for Installation of Backflow Prevention Assemblies on Landscape Irrigation Systems. Copies are available at the Tacoma Water permit counter or by calling (253) 502-8207.

14. Assemblies must be installed with proper clearance for testing and maintenance purposes.

Requirements for Specific Assemblies

Reduced Pressure Backflow Assemblies (RPBA)

1. RPBA’s cannot be installed in a vault or below ground unless specifically approved in writing by Tacoma Water.

2. An RPBA must have provisions that allow for safe and proper drainage.

3. A minimum one-inch air separation must be maintained below the relief valve port. Larger separations may be required depending on the size of the assembly.

Pressure Vacuum Breaker Assemblies (PVBA)

1. PVBAs must be installed a minimum of 12 inches above the highest downstream point.

2. PVBAs must be installed in a vertical configuration.

3. Compressed air fittings cannot be used on a system using a PVBA as backflow protection.

Atmospheric Vacuum Breakers (AVB)
1. AVBs must be installed a minimum of six inches above the highest downstream point.

2. AVBs must be installed in a vertical configuration.

3. Compressed air fittings cannot be used on a system using an AVB as backflow protection.

4. There can be no control valves or shut off valves installed downstream of the AVB.

5. There must be one AVB for each zone of the system.

Premises Requiring Isolation by AG or RPBA

By nature of their business, some facilities pose a severe or high health cross-connection hazard. To protect the public's health, the businesses on this list are required to isolate their premises by AG or RPBA, as outlined in Washington State's WAC 246-290-490.

  • Agricultural (farms & dairies)
  • 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 and with chemical addition
  • Laboratories
  • Metal planting industries
  • Mortuaries
  • Petroleum processing or storage plants
  • Piers and docks
  • Radioactive material; processing plants or nuclear reactors
  • Survey access denied or restricted
  • Wastewater lift stations and pumping stations
  • Wastewater treatment plants
  • Premises with an unapproved auxiliary water supply interconnected with the potable water supply