Backflow Assemblies

Backflow Overview

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. They are most commonly associated with fire sprinkler and irrigation systems.

The one-way check valve assemblies allow the water to only move forward into the system, not backwards into the water supply pipes that supply fresh water to homes and businesses. This is how backflow assemblies protect our water supply.

Types of Devices

The most common types of backflow device are:

  • Double Check Valve Assembly (DCVA)
  • Reduced Pressure Backflow Assembly (RPBA)
  • Atmospheric Vacuum Breaker (AVB)
  • Double Check Device Assembly (DCDA)
  • Pressure Reducing Valve (PRV)

Test Your Backflow System Annually

Annual testing of your backflow system is required by Washington State Code WAC 246-290-490 to assure that it is in perfect working order. The yearly test will identify any problems so they can be corrected. Please use the City of Issaquah form (PDF).

Each address within the City of Issaquah 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

Any state certified Backflow Assembly Tester (BAT) is able to perform this test. The City of Issaquah maintains a list of certified testers as a convenience to our customers. A copy of this list is included with the yearly mailing of your account information, test forms and due date.

These testers have requested that their company names appear on our current list. 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, contact the Washington State Department of Health at 800-525-2536 to confirm their certification.

Tokay WebTest Online Test Report Entry Transition

Beginning January 1, 2023, we will be transitioning all backflow test report submissions to the Tokay WebTest online platform. Test reports will no longer be received via mail, fax, or email. More information will be sent to testing companies and testers soon regarding this transition and WebTest access. 

Cost of Backflow System Test

The City of Issaquah does not possess information on costs of service for backflow assemblies. The most accurate way to obtain a current cost estimate is to call Backflow Assembly Testers and compare costs.


Please call us at 425-837-3470 to discuss any problems or concerns that you have with testing or the testing schedule. We are happy to work with you to resolve any difficulties.