Backflow Assembies Overview

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.

If you have an irrigation system for your yard, fire suppression sprinkler system, boiler, pool/spa or water feature, state law requires that you get a backflow prevention assembly from the USC-Approved Assemblies List to prevent contaminated water from flowing back into our drinking water system — a serious health hazard.

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 Duvall Form and have the completed reports submitted by September 1st of each year. Reminder letters are mailed once a year in June for the devices that are due to be tested.

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. A of certified testers is available here. as a convenience to our customers. 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.

The City of Duvall 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.

Why Testing is Required

Even the best backflow assembly can fail because of freezing, debris, improper installation and unapproved plumbing connections. That's why state law requires that backflow assemblies be tested annually by a certified backflow assembly tester to ensure that the assemblies will function if there is a backflow event.


Please call at 425-788-3434 or email us 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.

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)
Backflow Diagram


Cross Connection: a physical connection between drinkable water and a liquid or gas that could make the water unsafe to drink (wherever there is a cross connection, there is a potential threat to public health from the liquid or gas contaminants).

Backflow: water flowing in the opposite of its intended direction, either from a loss of pressure in the supply lines or an increase in pressure on the customer’s side (in either of these situations, if any affected customer’s pipes include a cross connection, contaminants could be drawn through the cross connection into that customer’s pipes—and, if the backflow continues, perhaps even into the water mains).