King County · System ID 40650 · Community water system
Is Highline Water District’s water safe? PFAS test results (King County, WA)
PFAS above Washington’s state action level
Highline Water District detected PFAS in 2 of its 3 tested water sources, with at least one result above Washington’s state action level (latest test November 2025).
Community water system serving King County · 29,544 connections · about 100,170 people.
At least one individual sample measured at or above a federal MCL value (4 ng/L for PFOA/PFOS; 10 ng/L for PFHxS, PFNA, HFPO-DA). Compliance with the federal standard is judged on running annual averages at the tap — a single source sample at that level is a flag, not a violation.
PFAS results on record for Highline Water District
| Analyte | Highest result | WA action level | Federal MCL | Detected at source |
|---|---|---|---|---|
| PFNA Perfluorononanoic acid | 13 ng/L above SAL | 9 ng/L | 10 ng/L | Tyee Well AFR835 |
| PFOS Perfluorooctanesulfonic acid | 5 ng/L | 15 ng/L | 4 ng/L | Tyee Well AFR835 |
| PFHxS Perfluorohexanesulfonic acid | 4 ng/L | 65 ng/L | 10 ng/L | McMicken Heights Well AEC950, Tyee Well AFR835 |
| PFBA Perfluorobutanoic acid | 2 ng/L | — | — | Tyee Well AFR835 |
| PFOA Perfluorooctanoic acid | 2 ng/L | 10 ng/L | 4 ng/L | Tyee Well AFR835 |
What this means
A Washington state action level (SAL) is the concentration at which the state requires a water system to notify its customers and take action — typically treating the affected source, blending it, or taking it offline. PFAS was detected in 2 of the 3 sources tested for this system, and at least one result was above a SAL. Ask the utility what it has done with the affected sources since the sample date — the table above shows which sources were affected.
For PFAS at the drinking tap, the fix we plan to offer is under-sink reverse osmosis — manufacturer test data shows RO membranes reduce PFAS. See the planned systems.
These results describe the water system’s sources (wells, intakes), not any individual tap — utilities blend, treat, and rotate sources. Data: Washington State Department of Health public PFAS results and Drinking Water Service Areas, dataset updated 2026-07-22. Latest test on record for this system: 2025-11-19. Informational only — not a certification of water quality and not health advice. If you have concerns about your drinking water, contact your utility or the WA DOH Office of Drinking Water.
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