Well water hardness in California
Across 52 counties of California, the median well sampled by the USGS has 9 gpg of hardness. Counties range from 2.6 gpg (El Dorado County) to 25.7 gpg (Santa Barbara County).
Millions of American households drink water from their own well. No utility tests that water and no water quality report covers it. These pages summarise the hardness the U.S. Geological Survey measured in wells county by county, so you know what to expect before you test your own well.
Counties, hardest first
| gpg | mg/L | wells | ||
|---|---|---|---|---|
| Santa Barbara County | 25.7 | 440 | 445 | very hard |
| San Luis Obispo County | 25.5 | 436 | 71 | very hard |
| Contra Costa County | 21.3 | 365 | 46 | very hard |
| San Mateo County | 18.6 | 318 | 39 | very hard |
| San Benito County | 18.1 | 310 | 35 | very hard |
| Alameda County | 17.7 | 303 | 209 | very hard |
| Orange County | 17.1 | 294 | 84 | very hard |
| Solano County | 16.4 | 281 | 84 | very hard |
| Colusa County | 15.9 | 273 | 21 | very hard |
| Santa Clara County | 15.5 | 265 | 73 | very hard |
| Monterey County | 14.7 | 251 | 90 | very hard |
| Stanislaus County | 14.6 | 250 | 210 | very hard |
| San Diego County | 14.5 | 249 | 362 | very hard |
| Yolo County | 14 | 240 | 127 | very hard |
| Sutter County | 13.7 | 234 | 39 | very hard |
| San Francisco County | 13.1 | 225 | 47 | very hard |
| Fresno County | 12.9 | 222 | 290 | very hard |
| Santa Cruz County | 12.9 | 220 | 158 | very hard |
| Riverside County | 11.9 | 204 | 651 | very hard |
| Glenn County | 11.7 | 201 | 36 | very hard |
| Los Angeles County | 11.6 | 198 | 687 | very hard |
| Lake County | 9.8 | 168 | 11 | hard |
| Imperial County | 9.4 | 160 | 86 | hard |
| San Joaquin County | 9.3 | 160 | 156 | hard |
| Humboldt County | 9.1 | 156 | 27 | hard |
| Tulare County | 9.1 | 155 | 173 | hard |
| Merced County | 9 | 154 | 250 | hard |
| Yuba County | 8.6 | 148 | 30 | hard |
| Kern County | 8.4 | 144 | 447 | hard |
| San Bernardino County | 7.6 | 130 | 1522 | hard |
| Mendocino County | 7.5 | 128 | 119 | hard |
| Trinity County | 7.4 | 127 | 12 | hard |
| Sonoma County | 7.2 | 124 | 129 | hard |
| Kings County | 7.1 | 121 | 98 | hard |
| Butte County | 6.6 | 113 | 68 | moderately hard |
| Tehama County | 6.5 | 112 | 110 | moderately hard |
| Siskiyou County | 6.5 | 111 | 40 | moderately hard |
| Amador County | 6.3 | 108 | 21 | moderately hard |
| Madera County | 5.6 | 97 | 118 | moderately hard |
| Sacramento County | 5.3 | 90 | 229 | moderately hard |
| Napa County | 5.2 | 88 | 55 | moderately hard |
| Mono County | 4.8 | 83 | 52 | moderately hard |
| Lassen County | 4.8 | 83 | 59 | moderately hard |
| Nevada County | 4.8 | 81 | 63 | moderately hard |
| Placer County | 4.6 | 79 | 109 | moderately hard |
| Shasta County | 4.3 | 74 | 87 | moderately hard |
| Inyo County | 4 | 68 | 93 | moderately hard |
| Modoc County | 4 | 68 | 18 | moderately hard |
| Calaveras County | 3.6 | 62 | 17 | moderately hard |
| Plumas County | 3.1 | 53 | 10 | soft |
| Mariposa County | 2.7 | 46 | 49 | soft |
| El Dorado County | 2.6 | 44 | 107 | soft |
Counties with fewer than 10 sampled wells, or a median outside 5–500 mg/L, are not shown until the figure is reviewed.
California: tap water hardness by city → · Well water hardness by state and county →