Measured, not modelled
Measured well-water hardness for California, county by county: the median of laboratory hardness samples taken at real water wells, in grains per gallon and mg/L as CaCO3, with the number of wells behind every figure.
Most published hardness-by-county tables are estimates from municipal tap water. The figures below are different: they are medians of laboratory samples taken at water wells, from the public record, and every row says how many wells stand behind it. The same table qualifies every lead Hard Water Feed sells, so this page is also how you check our arithmetic — the full method is on the methodology page.
Ratings below use the Water Quality Association scale, in grains per gallon (gpg); 1 gpg is 17.118 mg/L as CaCO3.
| Rating | Range |
|---|---|
| soft | 0 – 1 gpg |
| slightly hard | 1 – 3.5 gpg |
| moderately hard | 3.5 – 7 gpg |
| hard | 7 – 10.5 gpg |
| very hard | over 10.5 gpg |
Source: Water Quality Portal (USGS & US EPA). Water Quality Portal (USGS NWIS + EPA STORET), characteristic 'Hardness, Ca, Mg', siteType Well. 1109 local cells vs Texas's 4,296 — most leads will resolve at county level. 32 counties dropped for straddling the softener threshold. A county appears only when at least 3 distinct wells carry a laboratory hardness result; the 33 of California’s 58 counties not listed fall short of that bar or fall under the note above, and they are left out rather than guessed at.
| County | Median (gpg) | mg/L CaCO3 | Rating | Wells | Samples |
|---|---|---|---|---|---|
| Alameda | 18.1 | 310 | very hard | 267 | 267 |
| Alpine | 4.6 | 79 | moderately hard | 4 | 4 |
| Colusa | 11.7 | 200 | very hard | 164 | 164 |
| Contra Costa | 21.6 | 370 | very hard | 70 | 70 |
| Del Norte | 4.7 | 80 | moderately hard | 10 | 10 |
| Fresno | 19.3 | 330 | very hard | 1,459 | 1,459 |
| Glenn | 12.3 | 211 | very hard | 200 | 200 |
| Marin | 5.3 | 91 | moderately hard | 5 | 5 |
| Mariposa | 2.7 | 46 | slightly hard | 49 | 49 |
| Monterey | 17.5 | 300 | very hard | 291 | 291 |
| Orange | 12.9 | 221 | very hard | 473 | 473 |
| Plumas | 3.1 | 53 | slightly hard | 10 | 10 |
| San Benito | 18.5 | 317 | very hard | 36 | 36 |
| San Diego | 16.4 | 281 | very hard | 925 | 925 |
| San Francisco | 13.2 | 226 | very hard | 47 | 47 |
| San Luis Obispo | 38.4 | 657 | very hard | 151 | 151 |
| San Mateo | 19.4 | 332 | very hard | 41 | 41 |
| Santa Barbara | 31 | 531 | very hard | 1,587 | 1,587 |
| Santa Clara | 15.9 | 272 | very hard | 81 | 81 |
| Santa Cruz | 12.7 | 217 | very hard | 174 | 174 |
| Shasta | 4.2 | 72 | moderately hard | 151 | 151 |
| Solano | 15.8 | 270 | very hard | 125 | 125 |
| Stanislaus | 15.2 | 260 | very hard | 503 | 503 |
| Ventura | 31.6 | 541 | very hard | 301 | 301 |
| Yolo | 14.7 | 252 | very hard | 235 | 235 |
Yes — the median of 1,587 laboratory hardness samples from 1,587 measured wells in Santa Barbara County is 31 grains per gallon (about 531 mg/L as CaCO3), which is “very hard” on the Water Quality Association scale. This is groundwater measured at other wells in the county, not a reading from any one property.
Yes — the median of 1,459 laboratory hardness samples from 1,459 measured wells in Fresno County is 19.3 grains per gallon (about 330 mg/L as CaCO3), which is “very hard” on the Water Quality Association scale. This is groundwater measured at other wells in the county, not a reading from any one property.
Yes — the median of 925 laboratory hardness samples from 925 measured wells in San Diego County is 16.4 grains per gallon (about 281 mg/L as CaCO3), which is “very hard” on the Water Quality Association scale. This is groundwater measured at other wells in the county, not a reading from any one property.
Yes — the median of 503 laboratory hardness samples from 503 measured wells in Stanislaus County is 15.2 grains per gallon (about 260 mg/L as CaCO3), which is “very hard” on the Water Quality Association scale. This is groundwater measured at other wells in the county, not a reading from any one property.
Yes — the median of 473 laboratory hardness samples from 473 measured wells in Orange County is 12.9 grains per gallon (about 221 mg/L as CaCO3), which is “very hard” on the Water Quality Association scale. This is groundwater measured at other wells in the county, not a reading from any one property.
Yes — the median of 301 laboratory hardness samples from 301 measured wells in Ventura County is 31.6 grains per gallon (about 541 mg/L as CaCO3), which is “very hard” on the Water Quality Association scale. This is groundwater measured at other wells in the county, not a reading from any one property.
Yes — the median of 291 laboratory hardness samples from 291 measured wells in Monterey County is 17.5 grains per gallon (about 300 mg/L as CaCO3), which is “very hard” on the Water Quality Association scale. This is groundwater measured at other wells in the county, not a reading from any one property.
Yes — the median of 267 laboratory hardness samples from 267 measured wells in Alameda County is 18.1 grains per gallon (about 310 mg/L as CaCO3), which is “very hard” on the Water Quality Association scale. This is groundwater measured at other wells in the county, not a reading from any one property.
Yes — the median of 235 laboratory hardness samples from 235 measured wells in Yolo County is 14.7 grains per gallon (about 252 mg/L as CaCO3), which is “very hard” on the Water Quality Association scale. This is groundwater measured at other wells in the county, not a reading from any one property.
Yes — the median of 200 laboratory hardness samples from 200 measured wells in Glenn County is 12.3 grains per gallon (about 211 mg/L as CaCO3), which is “very hard” on the Water Quality Association scale. This is groundwater measured at other wells in the county, not a reading from any one property.
The answers above cover the 10 counties with the most measured wells; the table covers every county that clears the minimum. If your county isn’t listed, the honest answer is that the public record doesn’t hold enough well samples there for us to say — not that its water is soft.
Hard Water Feed publishes a weekly feed of newly filed domestic wells in these counties, qualified against this same hardness table and sold to one water-treatment business per territory. The territory grid shows what’s open; the category guide explains the mechanism.
Selling water treatment in California? The new wells behind these figures are sold by territory — well water leads in California.
Built from the same data that builds the feed, and regenerated with it — figures on this page change only when the underlying public record does.