Backflow FAQs

Press Enter to show all options, press Tab go to next option


Contact our Water Quality Office at (425) 398-4419 or


Is the backflow requirement a new law?

No, the WA State Administrative Code 246-290-490 requiring protection of public drinking water has been in effect for many years.  If you are just learning of the requirements, it means a recent District audit or other circumstance added your previously-unknown system to our records.

Why is the backflow test required annually?

Like any other mechanical device, over time a backflow unit may fail.  To ensure it is working properly to protect home and public drinking water systems, the law mandates an annual test.

Irrigation system box
Often irrigation system backflow devices will be located in a black or green box or can near the water meter.

Where is my backflow device located?

  • Irrigation system backflow units are most often located outside near your home or business water meter in a plastic box, usually green or black in color.
  • Fire sprinkler backflow units are also most often outside near the water meter, or they may be located in a garage.
  • Please note for all NEW backflow installations: District standard requires all new backflow devices to be installed directly behind the water meter (standard water detail #13).

What if I don't use my irrigation system any more, or it is broken.  Is the test still required?

Yes.  As long as an irrigation system is connected to the drinking water system - the potential for cross-contamination exists - the state law requires the annual test. 

Is there any way to avoid the test?

Man cutting irrigation system line with pipe cutting tool
Capping, or physically disconnecting your irrigation system, is the only way to be exempted from the requirement.

For irrigation systems, you may be exempted from the backflow test requirement if you physically disconnect (cap off) your irrigation system from the drinking water system.  Please note:  this is not the same thing as turning off your system for good.

If you plan to disconnect, contact us at to inspect the disconnection, or provide a photograph showing the disconnection.  If you performed the cut and cap previously, send us an email or letter indicating your service address and the approximate date the system was physically disconnected.

How much does a backflow test cost?

Costs vary between vendors.  The average range is between $50 and $80.  If you have your irrigation system regularly serviced, your irrigation professional may offer you a discount to combine the services.  Or you may be able to arrange a group of tests in your neighborhood at a discounted rate.

Does Northshore Utility District perform the test?

At this time, Northshore does not offer a backflow testing service.  Each property owner is responsible for contracting a certified backflow tester to perform the test and submit the satisfactory report to the District.

As a courtesy and for your convenience, we maintain a short list of certified testers authorized to do work in the area.  As a public agency, we cannot recommend any company over another.  We advise consulting reviews and getting more than one bid for service.

What do I do when the test is complete?

Your tester should submit the satisfactory test report to us on your behalf.  You should keep a copy for your records in case the report does not reach us.