County-by-county well water reports for California’s 58 counties, built from 191,000+ groundwater lab results from 5,916 wells sampled since 2000 (USGS and EPA Water Quality Portal) and compared against the State Water Resources Control Board’s drinking water standards. Statewide, the typical sampled well has 9.9 gpg of hardness, 14% of wells exceed the 10 µg/L arsenic limit, 9% exceed the 10 mg/L nitrate limit and 6% exceed California’s 10 µg/L hexavalent chromium limit.
Explore California well water by county
California Counties
All 58 California counties, A to Z. Counties marked “coming soon” are being added regularly.
- Alameda County coming soon
- Alpine County coming soon
- Amador County coming soon
- Butte County coming soon
- Calaveras County coming soon
- Colusa County coming soon
- Contra Costa County coming soon
- Del Norte County coming soon
- El Dorado County coming soon
- Fresno County coming soon
- Glenn County coming soon
- Humboldt County coming soon
- Imperial County coming soon
- Inyo County coming soon
- Kern County coming soon
- Kings County coming soon
- Lake County coming soon
- Lassen County coming soon
- Los Angeles County
- Madera County coming soon
- Marin County coming soon
- Mariposa County coming soon
- Mendocino County coming soon
- Merced County coming soon
- Modoc County coming soon
- Mono County coming soon
- Monterey County coming soon
- Napa County coming soon
- Nevada County coming soon
- Orange County
- Placer County coming soon
- Plumas County coming soon
- Riverside County
- Sacramento County coming soon
- San Benito County coming soon
- San Bernardino County
- San Diego County
- San Francisco County coming soon
- San Joaquin County coming soon
- San Luis Obispo County coming soon
- San Mateo County coming soon
- Santa Barbara County coming soon
- Santa Clara County
- Santa Cruz County coming soon
- Shasta County coming soon
- Sierra County coming soon
- Siskiyou County coming soon
- Solano County coming soon
- Sonoma County coming soon
- Stanislaus County coming soon
- Sutter County coming soon
- Tehama County coming soon
- Trinity County coming soon
- Tulare County coming soon
- Tuolumne County coming soon
- Ventura County coming soon
- Yolo County coming soon
- Yuba County coming soon
California Well Water Compared to the U.S.
| Share of wells with… | CaliforniaCA | United StatesUS |
|---|---|---|
| Hard water (above 7 gpg) | 64% | 60% |
| Iron above 0.3 mg/L | 9% | 19% |
| Manganese above 0.05 mg/L | 22% | 21% |
| Dissolved solids above 500 mg/L | 38% | 15% |
| Acidic water (pH below 6.5) | 2% | 14% |
| Nitrate above 10 mg/L (EPA limit) | 9% | 4% |
| Arsenic above 10 µg/L (EPA limit) | 14% | 7% |
| Chromium-6 above 10 µg/L (California limit) | 6% | — |
| Median hardness | 9.9 gpg | — |
| Median pH | 7.6 | 7.3 |
California: share of sampled wells (all well types, samples since 2000) whose typical value exceeds the level, from the Water Quality Portal. United States: USGS Circular 1332, about 2,100 domestic wells in 48 states sampled 1991 to 2004. Well types and years differ, so read this as a broad comparison.
California law lets some local sewer and water recycling agencies limit salt-discharging water softeners (Water Code Section 13148), so check local rules before installing one. Use the free well water diagnostic calculator to turn your own test results into a treatment plan.