Backflow Assemblies

What is a Backflow Assembly? Backflow Assembly

A backflow assembly is a device incorporated into your plumbing system with one-way valves that prevent potentially contaminated water from entering the drinking water system of a dwelling or the City water supply. The one-way check valve assemblies allow the water to only move forward into the system and not backward into the water supply pipes that supply fresh water to homes and businesses. This is how backflow assemblies protect our water supply.

Backflow assemblies are commonly associated with fire sprinkler and irrigation systems. Other applications seen throughout the City include boilers, pools, and even some humidifiers. These assemblies help us ensure the drinking water in Snoqualmie is safe and pleasant for all residents. All irrigation systems MUST have a backflow assembly installed.

  1. Back Siphonage
  2. Backpressure
  3. Prevention

Back siphonage is caused by negative pressure in the supply line to a facility or plumbing fixture. Backsiphonage may occur during waterline breaks, when repairs are made to the waterlines, and when shutting off the water supply.

City of Stanwood Approved Devices

  • Double Check Valve Assembly (DCVA)
  • Reduced Pressure Backflow Assembly (RPBA)

Why do I have to have a Backflow Assembly, and why do I have to have an annual test? 

All community water systems shall comply with the cross-connection control requirements set forth in WAC 246-290-490. Annual testing is required by the Washington State Department of Health through WAC 246-290-490 (iv). The tests must be performed annually, and any identified problems must be corrected immediately. 

Each address within the City of Stanwood that contains a backflow device is assigned an account number and a yearly due date for inspection of that device. Reminder letters are mailed each month for the devices that are due to be tested, along with detailed account information.

If an annual test is not performed, we will be required to terminate the water service at that particular address. Water service will only be restored when the backflow devices are in compliance with Washington State codes.

Failed Backflow Tests

If your backflow system fails the test, repairs must be performed immediately. A backflow assembly that has failed will not protect our water supply. The tester you have hired will be able to assist you with this issue. Your account cannot be considered current unless or until each backflow assembly has passed the tests.

Certified Backflow Assembly Testers

We have a list of Backflow Assembly Testers (BATs) that have requested their company names appear on our current list. You can email for a current list of certified testers. This list does not include all certified BATs and is not a recommendation to hire. If you wish to hire an individual whose name does not appear on this list, you can visit BAT Certification Status - Washington Certification Services ( to verify certifications or search for a tester who is certified to test in Snohomish County. 

More Information: 

Do I need to have a Backflow Device Installed? Visit WAC 246-290-490: or Contact


Please send any questions about test due dates, assembly locations, or backflow assemblies to