Mercer Island · King County
Backflow testing on Mercer Island — including boat lifts
Mercer Island tracks every irrigation system and backflow assembly on the island and mails an annual letter when your test is due. Lakefront homes often have more than one — irrigation, fire sprinklers, even water-powered boat lifts. We test them all in one visit.
Mercer Island program
How Mercer Island’s backflow program works
The short version, summarized from the utility’s own cross-connection control materials.
Source: City of Mercer Island · verified October 2026 ↗The City sends an annual letter when your backflow assembly is due for testing.
Testing must be done by a state-certified backflow tester.
The City’s program specifically calls out cross-connections like irrigation systems and boat lifts — not just commercial plumbing.
Report submission
Testers file completed reports through the City’s online Tokay test portal. New-installation reports may be emailed to the City.
Questions for the utility: backflow@mercerisland.gov · (206) 275-7608
On the ground
What we see in Mercer Island
Every city’s housing stock and commercial mix shapes what’s in the meter box.
Water-powered boat lifts
Hydraulic boat lifts that run on city water pressure are a cross-connection with Lake Washington. They need proper backflow protection and a yearly test — and they’re often the assembly people forget.
Services in Mercer Island
Neighborhoods
Serving all of Mercer Island
- North End
- Town Center
- East Seattle
- First Hill
- Mercerdale
- Mercerwood
- South End
- Westside
- Eastside
FAQ
Mercer Island backflow questions
01 Who can test my backflow assembly in Mercer Island?
02 How do backflow test reports get submitted to Mercer Island?
03 How much does backflow testing cost in Mercer Island?
04 What if my assembly fails in Mercer Island?
Field test report · next due
Mercer Island test due? We’ll handle it.
Book online in two minutes. We test, repair if needed, and file the report with your water utility — and remind you next year.