Water quality by county
in California
EPA sampled public water systems across California for PFAS under its UCMR 5 programme. Of the 58 counties, 35 have a reading above a federal limit and 1 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 |
|---|---|---|---|
| San Bernardino County | 2,214,281 | 59× | PFOS · 236.5 ng/L |
| San Diego County | 3,298,799 | 47× | PFOA · 188.3 ng/L |
| Los Angeles County | 9,757,179 | 15× | PFOS · 59 ng/L |
| Merced County | 296,774 | 11× | PFOS · 45 ng/L |
| Sacramento County | 1,611,231 | 10× | PFOS · 41.4 ng/L |
| Fresno County | 1,024,125 | 10× | PFOS · 41 ng/L |
| San Luis Obispo County | 281,843 | 8.3× | PFOS · 33 ng/L |
| Riverside County | 2,529,933 | 7.8× | PFOS · 31.4 ng/L |
| Orange County | 3,170,435 | 7.3× | PFOS · 29 ng/L |
| Alameda County | 1,649,060 | 6.5× | PFOS · 26 ng/L |
| Stanislaus County | 556,972 | 6.5× | PFOS · 26 ng/L |
| Tulare County | 483,546 | 5.8× | PFOS · 23 ng/L |
| Butte County | 208,334 | 5.6× | PFOS · 22.5 ng/L |
| Trinity County | 15,642 | 4.8× | PFOS · 19 ng/L |
| Kern County | 922,529 | 4.7× | PFOA · 18.6 ng/L |
| San Joaquin County | 816,108 | 4.3× | PFOS · 17 ng/L |
| Ventura County | 835,427 | 4.3× | PFOS · 17 ng/L |
| Shasta County | 181,121 | 4.0× | PFOA · 16.2 ng/L |
| Napa County | 132,727 | 3.0× | PFOS · 12.2 ng/L |
| Yuba County | 87,469 | 2.8× | PFOS · 11 ng/L |
| Solano County | 455,101 | 2.5× | PFOS · 10 ng/L |
| San Mateo County | 742,893 | 2.4× | PFOA · 9.6 ng/L |
| Monterey County | 436,251 | 2.0× | PFOA · 8.1 ng/L |
| Santa Clara County | 1,926,325 | 2.0× | PFOA · 8 ng/L |
| Madera County | 165,432 | 2.0× | PFOS · 7.9 ng/L |
| Mendocino County | 89,175 | 1.9× | PFOS · 7.4 ng/L |
| Tehama County | 64,451 | 1.9× | PFOA · 7.4 ng/L |
| Santa Cruz County | 262,406 | 1.6× | PFOA · 6.5 ng/L |
| Sonoma County | 485,375 | 1.6× | PFOA · 6.2 ng/L |
| El Dorado County | 192,823 | 1.5× | PFOA · 6.1 ng/L |
| Tuolumne County | 53,893 | 1.2× | PFOS · 4.9 ng/L |
| Nevada County | 102,195 | 1.1× | PFOA · 4.6 ng/L |
| San Benito County | 69,159 | 1.1× | PFOA · 4.6 ng/L |
| Placer County | 433,822 | 1.1× | PFOS · 4.3 ng/L |
| San Francisco County | 827,526 | 1.0× | PFOA · 4 ng/L |
| Yolo County | 225,251 | under the limit | PFNA · 4.2 ng/L |
| Modoc County | 8,491 | under the limit | PFHxS · 3.5 ng/L |
| Alpine County | 1,099 | under the limit | — |
| Amador County | 42,026 | under the limit | — |
| Calaveras County | 46,505 | under the limit | — |
| Colusa County | 22,074 | under the limit | — |
| Contra Costa County | 1,172,607 | under the limit | — |
| Del Norte County | 27,009 | under the limit | — |
| Glenn County | 28,304 | under the limit | — |
| Humboldt County | 132,380 | under the limit | — |
| Imperial County | 181,724 | under the limit | — |
| Inyo County | 18,485 | under the limit | — |
| Kings County | 154,913 | under the limit | — |
| Lake County | 67,764 | under the limit | — |
| Lassen County | 28,340 | under the limit | — |
| Marin County | 256,400 | under the limit | — |
| Mariposa County | 17,048 | under the limit | — |
| Mono County | 12,991 | under the limit | — |
| Plumas County | 18,834 | under the limit | — |
| Santa Barbara County | 444,500 | under the limit | — |
| Sierra County | 3,113 | not sampled | — |
| Siskiyou County | 42,498 | under the limit | — |
| Sutter County | 98,545 | under the limit | — |