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Not health advice. Contact your local water utility for concerns.
Data from EPA Water Quality Reports. For official information, contact your water utility or health department.
Compare water quality across 33 counties in California
33 counties ranked by average water quality score
| Rank | County | Avg Score | Grade | Cities | Population | Score Range |
|---|---|---|---|---|---|---|
| 1 | Contra Costa County | 100 | A | 5 | 538,863 | 100 - 100 |
| 2 | Ventura County | 100 | A | 4 | 394,951 | 99 - 100 |
| 3 | San Mateo County | 100 | A | 4 | 313,554 | 100 - 100 |
| 4 | Sonoma County | 100 | A | 2 | 236,177 | 100 - 100 |
| 5 | Placer County | 100 | A | 1 | 155,612 | 100 - 100 |
| 6 | Napa County | 100 | A | 1 | 84,804 | 100 - 100 |
| 7 | Sutter County | 100 | A | 1 | 70,256 | 100 - 100 |
| 8 | Madera County | 100 | A | 1 | 66,560 | 100 - 100 |
| 9 | Marin County | 100 | A | 1 | 61,691 | 100 - 100 |
| 10 | Imperial County | 100 | A | 1 | 43,772 | 100 - 100 |
| 11 | Santa Barbara County | 99 | A | 2 | 208,800 | 97 - 100 |
| 12 | Kings County | 99 | A | 1 | 62,127 | 99 - 99 |
| 13 | San Diego County | 97 | A | 11 | 2,734,270 | 74 - 100 |
| 14 | Monterey County | 97 | A | 1 | 123,679 | 97 - 97 |
| 15 | Sacramento County | 94 | A | 6 | 808,933 | 74 - 100 |
| 16 | Santa Clara County | 93 | A | 8 | 1,634,276 | 64 - 100 |
| 17 | Riverside County | 92 | A | 10 | 2,047,641 | 71 - 100 |
| 18 | San Luis Obispo County | 92 | A | 2 | 78,964 | 84 - 100 |
| 19 | Alameda County | 90 | A | 6 | 2,185,633 | 68 - 100 |
| 20 | Yolo County | 90 | A | 3 | 182,274 | 69 - 100 |
| 21 | Orange County | 89 | B | 20 | 2,853,878 | 73 - 100 |
| 22 | Santa Cruz County | 87 | B | 2 | 159,857 | 74 - 100 |
| 23 | Los Angeles County | 86 | B | 37 | 7,554,782 | 65 - 100 |
| 24 | Solano County | 82 | B | 3 | 341,447 | 69 - 100 |
| 25 | Kern County | 82 | B | 2 | 319,309 | 74 - 90 |
| 26 | San Bernardino County | 81 | B | 14 | 1,399,075 | 34 - 100 |
| 27 | Stanislaus County | 81 | B | 2 | 291,453 | 61 - 100 |
| 28 | San Joaquin County | 78 | C | 4 | 441,111 | 56 - 100 |
| 29 | Merced County | 76 | C | 1 | 93,692 | 76 - 76 |
| 30 | Butte County | 74 | C | 1 | 114,925 | 74 - 74 |
| 31 | Shasta County | 74 | C | 1 | 89,628 | 74 - 74 |
| 32 | Tulare County | 72 | C | 3 | 284,224 | 43 - 100 |
| 33 | Fresno County | 71 | C | 2 | 675,846 | 71 - 71 |
5 cities • 538,863 residents
4 cities • 394,951 residents
4 cities • 313,554 residents
11 cities • 2,734,270 residents
6 cities • 808,933 residents
8 cities • 1,634,276 residents
10 cities • 2,047,641 residents
6 cities • 2,185,633 residents
20 cities • 2,853,878 residents
37 cities • 7,554,782 residents
2 cities • 319,309 residents
14 cities • 1,399,075 residents
See all 33 counties in the ranking table above
Our county-level water quality analysis aggregates data from municipal water systems across California. Each county's score represents the average water quality across all analyzed cities within that county, weighted by population served.
With 33 counties and 163 cities analyzed, this data helps residents understand regional water quality patterns in California. County scores range from 34/100 to 100/100, reflecting the diversity of water sources and treatment infrastructure across the state.
All analyzed counties in California maintain average scores above 70, indicating generally acceptable water quality standards statewide. Individual city scores may vary, so residents should still review their specific city's report.