California water quality by county
58 counties with public water systems. Pick a county to see every system that serves it.
| County | Active systems | People served | Share with violations, 3 yr | Serious violators | Health flags |
|---|---|---|---|---|---|
| Alameda County | 27 | 2,273,899 | 0 | 2 | |
| Alpine County | 40 | 15,793 | 0 | 2 | |
| Amador County | 68 | 39,147 | 0 | 3 | |
| Butte County | 89 | 227,378 | 0 | 24 | |
| Calaveras County | 48 | 55,628 | 0 | 3 | |
| Colusa County | 28 | 35,510 | 0 | 0 | |
| Contra Costa County | 84 | 582,859 | 0 | 8 | |
| Del Norte County | 32 | 28,172 | 1 | 7 | |
| El Dorado County | 128 | 215,892 | 3 | 3 | |
| Fresno County | 339 | 1,005,373 | 0 | 37 | |
| Glenn County | 35 | 36,681 | 0 | 1 | |
| Humboldt County | 90 | 131,927 | 1 | 18 | |
| Imperial County | 79 | 191,946 | 0 | 24 | |
| Inyo County | 115 | 100,496 | 0 | 8 | |
| Kern County | 336 | 1,062,083 | 0 | 28 | |
| Kings County | 43 | 146,809 | 0 | 3 | |
| Lake County | 81 | 72,691 | 0 | 9 | |
| Lassen County | 56 | 23,250 | 0 | 4 | |
| Los Angeles County | 271 | 10,081,756 | 4 | 24 | |
| Madera County | 202 | 187,073 | 1 | 17 | |
| Marin County | 47 | 266,457 | 0 | 2 | |
| Mariposa County | 68 | 25,753 | 0 | 3 | |
| Mendocino County | 148 | 82,992 | 1 | 11 | |
| Merced County | 119 | 266,400 | 1 | 10 | |
| Modoc County | 16 | 5,067 | 0 | 3 | |
| Mono County | 91 | 110,574 | 1 | 6 | |
| Monterey County | 311 | 494,172 | 1 | 48 | |
| Napa County | 188 | 136,576 | 1 | 24 | |
| Nevada County | 84 | 102,602 | 0 | 4 | |
| Orange County | 46 | 3,204,616 | 0 | 3 | |
| Placer County | 122 | 432,847 | 1 | 5 | |
| Plumas County | 111 | 24,808 | 0 | 10 | |
| Riverside County | 198 | 2,719,341 | 0 | 24 | |
| Sacramento County | 164 | 1,657,158 | 0 | 22 | |
| San Benito County | 64 | 105,886 | 0 | 9 | |
| San Bernardino County | 321 | 2,573,235 | 1 | 24 | |
| San Diego County | 198 | 3,535,829 | 1 | 11 | |
| San Francisco County | 8 | 899,318 | 0 | 0 | |
| San Joaquin County | 306 | 794,026 | 0 | 21 | |
| San Luis Obispo County | 172 | 292,764 | 0 | 9 | |
| San Mateo County | 51 | 776,653 | 0 | 3 | |
| Santa Barbara County | 151 | 653,638 | 0 | 11 | |
| Santa Clara County | 119 | 2,074,486 | 0 | 11 | |
| Santa Cruz County | 95 | 272,474 | 0 | 20 | |
| Shasta County | 176 | 208,824 | 0 | 31 | |
| Sierra County | 33 | 6,719 | 0 | 1 | |
| Siskiyou County | 72 | 40,976 | 1 | 16 | |
| Solano County | 64 | 472,818 | 0 | 7 | |
| Sonoma County | 445 | 470,466 | 0 | 42 | |
| Stanislaus County | 192 | 506,514 | 1 | 19 | |
| Sutter County | 35 | 87,542 | 0 | 0 | |
| Tehama County | 111 | 50,713 | 0 | 37 | |
| Trinity County | 44 | 14,588 | 0 | 9 | |
| Tulare County | 290 | 463,870 | 0 | 46 | |
| Tuolumne County | 120 | 76,382 | 0 | 11 | |
| Ventura County | 95 | 875,995 | 0 | 17 | |
| Yolo County | 88 | 224,609 | 0 | 11 | |
| Yuba County | 66 | 110,070 | 0 | 2 |
under 30% 30 to 59% 60% and over
About this data
Share with violations counts any violation in the past three years, including monitoring and reporting lapses. Counts cover active systems; systems serving more than one county are counted in each.
Source: the U.S. EPA's Enforcement and Compliance History Online system (ECHO), which publishes the federal Safe Drinking Water Information System. EPA's terms and values are shown as published. The California records are from EPA's data refresh of Oct 7, 2026; EPA refreshes this data quarterly, and states report to EPA with a lag of three to six months, so the newest violations may not appear yet. Retrieved from ECHO on Oct 11, 2026.