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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 34 counties in California
34 counties ranked by average water quality score
| Rank | County | Avg Score | Grade | Cities | Population | Score Range |
|---|---|---|---|---|---|---|
| 1 | Kings County | 96 | A+ | 1 | 57,232 | 96 - 96 |
| 2 | Stanislaus County | 88 | A- | 2 | 292,095 | 85 - 91 |
| 3 | Marin County | 87 | A- | 2 | 120,444 | 86 - 87 |
| 4 | Sacramento County | 86 | A- | 7 | 1,127,872 | 80 - 94 |
| 5 | San Luis Obispo County | 86 | A- | 2 | 79,952 | 82 - 89 |
| 6 | San Francisco County | 86 | A- | 1 | 873,965 | 86 - 86 |
| 7 | Imperial County | 85 | A- | 1 | 43,363 | 85 - 85 |
| 8 | Napa County | 85 | A- | 1 | 79,263 | 85 - 85 |
| 9 | San Joaquin County | 84 | B+ | 4 | 564,841 | 71 - 96 |
| 10 | Solano County | 84 | B+ | 3 | 343,520 | 72 - 93 |
| 11 | Santa Barbara County | 84 | B+ | 2 | 195,928 | 71 - 96 |
| 12 | Sutter County | 84 | B+ | 1 | 70,117 | 84 - 84 |
| 13 | San Mateo County | 83 | B+ | 4 | 362,186 | 81 - 88 |
| 14 | Sonoma County | 83 | B+ | 2 | 239,506 | 71 - 94 |
| 15 | Shasta County | 83 | B+ | 1 | 92,590 | 83 - 83 |
| 16 | Monterey County | 83 | B+ | 1 | 163,542 | 83 - 83 |
| 17 | Los Angeles County | 82 | B+ | 43 | 8,073,337 | 58 - 96 |
| 18 | San Bernardino County | 82 | B+ | 15 | 1,694,432 | 45 - 93 |
| 19 | Butte County | 82 | B+ | 1 | 101,475 | 82 - 82 |
| 20 | Tulare County | 81 | B+ | 3 | 265,670 | 75 - 86 |
| 21 | Orange County | 80 | B+ | 24 | 2,803,455 | 54 - 98 |
| 22 | Contra Costa County | 79 | B | 8 | 694,267 | 65 - 89 |
| 23 | Ventura County | 79 | B | 5 | 636,053 | 49 - 96 |
| 24 | Riverside County | 78 | B | 15 | 1,683,676 | 47 - 97 |
| 25 | Fresno County | 78 | B | 2 | 662,231 | 74 - 82 |
| 26 | Santa Clara County | 77 | B | 8 | 1,646,854 | 47 - 93 |
| 27 | San Diego County | 76 | B | 13 | 2,696,875 | 45 - 96 |
| 28 | Alameda County | 76 | B | 10 | 1,446,468 | 44 - 90 |
| 29 | Placer County | 74 | B- | 2 | 219,102 | 73 - 74 |
| 30 | Yolo County | 69 | C+ | 3 | 184,793 | 50 - 86 |
| 31 | Santa Cruz County | 69 | C+ | 2 | 116,956 | 68 - 69 |
| 32 | Merced County | 69 | C+ | 1 | 86,333 | 69 - 69 |
| 33 | Kern County | 68 | C+ | 2 | 455,175 | 67 - 68 |
| 34 | Madera County | 67 | C+ | 1 | 66,700 | 67 - 67 |
7 cities • 1,127,872 residents
1 cities • 873,965 residents
4 cities • 564,841 residents
4 cities • 362,186 residents
43 cities • 8,073,337 residents
15 cities • 1,694,432 residents
24 cities • 2,803,455 residents
8 cities • 694,267 residents
5 cities • 636,053 residents
15 cities • 1,683,676 residents
2 cities • 662,231 residents
8 cities • 1,646,854 residents
See all 34 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 34 counties and 193 cities analyzed, this data helps residents understand regional water quality patterns in California. County scores range from 44/100 to 98/100, reflecting the diversity of water sources and treatment infrastructure across the state.
Currently, 5 counties in California have average scores below 70, indicating potential water quality concerns. Residents in these areas should review their city's specific report and consider water filtration options.