Backflow Assembly

To ensure that the water system is properly protected and that all system users receive safe drinking water, the Liberty Lake Sewer and Water District (LLSWD) requires that all customers (residential, multifamily and commercial) test their backflow assemblies annually. Annual backflow assembly testing is required to ensure proper function of the assembly and protection of the water system. Testing must be performed by a Washington State Certified Backflow Assembly Tester and must be completed by June 30 annually.

2021 marks the first year of the annual testing requirement for our residential customers. Below are a few common questions we received.

Backflow FAQ

  1. Why does my assembly have to be tested annually?

    Once water enters your sprinkler system it is no longer potable (drinking) water as it can become contaminated with pesticides, herbicides, fertilizers and animal waste. These contaminants can enter the sprinkler system and water supply through broken sprinkler lines or heads, fall sprinkler blow out, or a high demand event (such as a broken water main) on the public water system. If a backflow assembly is absent, not installed properly, or is not functioning properly, contaminated water from the sprinkler system can be forced back into your home’s water supply and/or the public water system.

    Backflow assemblies are mechanical devices. For proper operation, regular and routine maintenance is necessary. Similarly for your automobile, heating and cooling units, lawn mowers, etc. Why shouldn’t the same apply to your backflow assembly? Backflow assemblies are manufactured with internal checks and O-rings that are made with a different variety of rubber compounds. Combine that with either a hard or soft water and you will get varying degrees of performance. Some check discs simply will not hold up under hard water conditions. Some assembly bodies are susceptible to scaling and severe rusting that will foul the checks. Backflow assemblies may collect sand and debris causing fouling. In the Pacific Northwest we have to winterize our irrigation systems annually. Improper sprinkler system blowout with excessive pressure and/or water left in the backflow assembly can cause damage from water freezing and expanding. All of these factors are the reason that an ongoing maintenance and testing program is necessary for proper operation.

    Because backflow assemblies are mechanical devices and their design and operation can fail, manufacturers recommend that annual testing be performed, especially since these devices are designed to protect the water supply. As such, state and local cross connection regulations require a testing schedule, with the vast majority dictating annual testing.

  2. What percentage of devices fail?

    According to actual test results received by the District in 2021 the percentage of failed residential backflow assembly tests is 42.5%. That means that nearly one out of two backflow assemblies failed their initial testing. These data only include the failed test reports that were actually submitted to the District. Other failures or absence of backflow assemblies where a report was not submitted were not counted as part of the failed percentage.
  3. Repair or Replace: Why do I have to replace my device? Can it be repaired?

    There are many conditions that can shorten the life of a backflow assembly. Conditions such as overwintering (freezing), improper blow out (excessive pressure), debris in the irrigation lines such as dirt and sand, and water quality (hard water) can all cause the assembly to deteriorate in its performance.

    The purpose of a repair on a backflow assembly is to return the assembly back to its original factory working specifications. The need for a repair can only be determined by conducting a test on the assembly and knowing when the data indicates the backflow prevention assembly is in need of repair. Backflow assemblies should only be repaired when the data collected from the test indicates the assembly has degraded in its performance below an established minimum standard. The test procedure is a diagnostic evaluation of the workings of a backflow assembly. When the backflow assembly fails to meet this minimum standard, the backflow assembly must be repaired or if necessary, replaced. In some instances the backflow assembly may be too old where parts are not available to conduct a repair and the backflow assembly must be replaced.

  4. Why do I have to have to test a newly installed backflow assembly?

    Although a brand new backflow assembly is intended to work directly off the shelf, incorrect installation may cause the device to fail. The installing contractor may not flush out the line and pipe cutting debris, and dirt and sand can inadvertently enter the irrigation pipe during installation. If debris gets into the seat of the relief valve it prevents the valve from shutting all the way causing the device to fail the test.

  5. Backflow test reports: Who sends them in?

    The certified backflow assembly tester will complete the test and will typically submit the test report to the District on behalf of the customer. In some instances the customer may receive a copy or will be responsible for submitting the report. It is important to verify with the backflow assembly tester who is responsible for submitting the test report. You can always contact the District to verify if your test report has been received.

For educational purposes on backflow assemblies we’ve created a demonstration display at our office – come visit. For more information on our program, please visit the LLSWD’s Cross-Connection Control Program webpage for requirements, additional education resources, and a list of some local, Washington State Certified Backflow Assembly Testers at If you have questions, please call LLSWD at (509) 922-5443 or email us at

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