No PFAS were detected in any of the 4 samples EPA's program collected.
King County Water District #20 is a public water system drawing on surface water, based in Seattle, Washington, serving about 48,469 people. Under EPA's Fifth Unregulated Contaminant Monitoring Rule it was tested for 29 PFAS and lithium 4 times across 1 sampling point between Mar 2024 and Dec 2024.
None of the 29 PFAS were found at or above EPA's minimum reporting levels (2 to 20 ppt depending on the compound).
Not detected: PFTrDA, 6:2 FTS, 8:2 FTS, PFMPA, PFPeA, PFMBA, PFBS, NEtFOSAA, 9Cl-PF3ONS, PFTA, PFEESA, HFPO-DA, PFHpS, PFPeS, NMeFOSAA, PFOA, PFHpA, 4:2 FTS, PFHxS, PFNA, PFBA, PFOS, ADONA, PFDA, PFDoA, PFHxA, PFUnA, 11Cl-PF3OUdS, NFDHA.
Lithium, tested in the same program: not detected.
In April 2024 EPA set enforceable limits of 4 ppt for PFOA and PFOS, 10 ppt each for PFHxS, PFNA and GenX, and a hazard index of 1 for mixtures. Utilities were given until 2029 to comply. In May 2026 EPA proposed keeping only the PFOA and PFOS limits and moving that deadline to 2031. Until that proposal is final, the 2024 limits stand.
Compliance is judged on a running annual average at each entry point, so we show the average at this system's worst sampling point next to its single highest result. UCMR 5 results do not by themselves put a utility in or out of compliance.
No PFAS action is needed on these results. If your water tastes or smells of chlorine, a whole-house city water filter is the usual fix.
All 248 tested systems in Washington
98108 98146 98148 98166 98168
As reported by the utility to EPA. Neighbouring ZIPs are often split between systems; your water bill names yours.
Well & Tap. "PFAS in King County Water District #20 water: EPA UCMR 5 results." Data: U.S. EPA Fifth Unregulated Contaminant Monitoring Rule, final release August 2026, PWSID WA5338950. https://wellandtap.com/pfas/washington/king-county-water-district-20/
Source: U.S. EPA, UCMR 5 occurrence data, final release August 2026 (PWSID WA5338950). Population: EPA SDWIS. Averages count results below the reporting level as zero, the same convention EPA uses for running annual averages. Full method.
