Water quality by county
in Washington
EPA sampled public water systems across Washington for PFAS under its UCMR 5 programme. Of the 39 counties, 10 have a reading above a federal limit and 6 have not been sampled at all — which is not a clean result, only an absence of one. Each county below shows what was found, at what concentration, and at which utility.
| county | Population | Worst result | Compound |
|---|---|---|---|
| Pierce County | 941,170 | 38× | PFOS · 153.6 ng/L |
| Grant County | 104,717 | 13× | PFOS · 52.2 ng/L |
| Clark County | 527,269 | 4.7× | PFOS · 18.6 ng/L |
| Benton County | 218,190 | 4.3× | PFOS · 17 ng/L |
| Spokane County | 555,947 | 3.0× | PFOS · 12 ng/L |
| King County | 2,340,211 | 2.8× | PFOS · 11.1 ng/L |
| Island County | 86,478 | 2.5× | PFOA · 9.8 ng/L |
| Lewis County | 87,049 | 1.4× | PFOS · 5.8 ng/L |
| Thurston County | 302,912 | 1.4× | PFOS · 5.8 ng/L |
| Kitsap County | 281,420 | 1.4× | PFOA · 5.7 ng/L |
| Snohomish County | 864,113 | under the limit | PFHxS · 4.9 ng/L |
| Adams County | 21,039 | under the limit | — |
| Asotin County | 22,523 | under the limit | — |
| Chelan County | 81,228 | under the limit | — |
| Clallam County | 77,958 | under the limit | — |
| Columbia County | 4,025 | not sampled | — |
| Cowlitz County | 113,982 | under the limit | — |
| Douglas County | 45,795 | under the limit | — |
| Ferry County | 7,543 | not sampled | — |
| Franklin County | 101,238 | under the limit | — |
| Garfield County | 2,404 | not sampled | — |
| Grays Harbor County | 77,893 | under the limit | — |
| Jefferson County | 33,944 | under the limit | — |
| Kittitas County | 48,172 | under the limit | — |
| Klickitat County | 24,124 | under the limit | — |
| Lincoln County | 11,862 | under the limit | — |
| Mason County | 69,632 | under the limit | — |
| Okanogan County | 44,942 | under the limit | — |
| Pacific County | 24,245 | under the limit | — |
| Pend Oreille County | 14,332 | not sampled | — |
| San Juan County | 18,668 | under the limit | — |
| Skagit County | 132,736 | under the limit | — |
| Skamania County | 12,660 | not sampled | — |
| Stevens County | 49,015 | under the limit | — |
| Wahkiakum County | 4,800 | not sampled | — |
| Walla Walla County | 62,068 | under the limit | — |
| Whatcom County | 234,954 | under the limit | — |
| Whitman County | 48,399 | under the limit | — |
| Yakima County | 258,523 | under the limit | — |