Free or low-cost state testing
The State and Regional Water Boards fund or regulate 11 domestic well programs that offer free well testing in their service areas.
State Water Resources Control Board: private well testingGetting your well water tested in California
California has free or low-cost well testing. Across the state, the ones worth testing for are arsenic, nitrate, manganese and uranium, plus bacteria every year.
About 2,185,000 people in California get their water from a private well, about 1 in 18 residents.
Three ways to get tested, cheapest first.
A lab California certifies
The state's list of labs certified for drinking water. Many sell bottles you pick up or get by mail, and their results count for a home sale or loan.
Labs certified by CaliforniaA mail-in kit
Order online, fill the bottles at your kitchen tap and get results by email in about a week. Full well tests run about $210 to $220.
Compare kits for CaliforniaWhat turns up in California wells.
Share of tested wells over the limit, from lab tests the USGS, EPA and state agencies collected since 2000. Your own well needs its own test.
Arsenic14%652 of 4,520Nitrate10%461 of 4,733Manganese8%386 of 4,639Uranium8%254 of 3,360Radon3%34 of 1,015Fluoride3%125 of 4,619Leadunder 1%12 of 2,851
GermsTest every year, whatever the chart says
Coliform bacteria21%236 of 1,133StainsNot a health risk
Iron stains10%469 of 4,656
Rare: under 5%Worth checking: 5 to 15%Widespread: 15%+
Lab results: Water Quality Portal (USGS and EPA)
Where it shows up most
- Nitrate shows up most in Tulare County (about 4 in 10 wells), Merced County (about 3 in 10 wells), Fresno County (about 3 in 10 wells).
- Arsenic shows up most in Mono County (about 5 in 10 wells), Kings County (about 5 in 10 wells), San Joaquin County (about 3 in 10 wells).
- Uranium shows up most in Fresno County (about 1 in 4 wells), Orange County (about 1 in 4 wells), Kings County (about 2 in 10 wells).
Find your county.
25 counties have a full report with local test results and well depths.
ButteEl DoradoFresnoKernLos AngelesMaderaMendocinoMercedMontereyNevadaOrangePlacerRiversideSacramentoSan BernardinoSan DiegoSan JoaquinSan Luis ObispoSanta CruzShastaSonomaStanislausTehamaTulareYolo
No full report for that county yet. The statewide results above still apply, and so do the three ways to get tested.
Every county in California: people on wells and typical depth
| County | People on private wells | Share of residents | Typical well depth |
|---|---|---|---|
| Riverside County | 227,221 | 9% | 280 ft |
| Fresno County | 149,804 | 15% | 180 ft |
| Los Angeles County | 113,474 | 1% | 320 ft |
| Sonoma County | 95,450 | 20% | 190 ft |
| San Diego County | 90,496 | 3% | 340 ft |
| Tulare County | 89,473 | 19% | 200 ft |
| San Bernardino County | 80,772 | 4% | 250 ft |
| Placer County | 79,205 | 20% | 200 ft |
| San Joaquin County | 74,887 | 10% | 220 ft |
| Stanislaus County | 68,139 | 12% | 172 ft |
| Kern County | 53,705 | 6% | 303 ft |
| El Dorado County | 53,523 | 28% | 250 ft |
| Merced County | 50,415 | 18% | 200 ft |
| Nevada County | 48,312 | 47% | 220 ft |
| Butte County | 47,277 | 22% | 150 ft |
| Madera County | 47,219 | 30% | 356 ft |
| Orange County | 45,836 | 1% | 204 ft |
| Monterey County | 43,611 | 10% | 300 ft |
| Sacramento County | 43,308 | 3% | 215 ft |
| Santa Cruz County | 40,932 | 15% | 245 ft |
| Yolo County | 40,521 | 19% | 197 ft |
| Tehama County | 38,995 | 59% | 160 ft |
| San Luis Obispo County | 38,848 | 14% | 330 ft |
| Mendocino County | 37,855 | 41% | 140 ft |
| Shasta County | 37,596 | 21% | 160 ft |
| Contra Costa County | 29,377 | 3% | 180 ft |
| Imperial County | 28,417 | 16% | 259 ft |
| Kings County | 26,988 | 18% | 216 ft |
| Yuba County | 25,165 | 31% | 197 ft |
| Santa Barbara County | 21,877 | 5% | 332 ft |
| Tuolumne County | 21,649 | 39% | 345 ft |
| Calaveras County | 21,588 | 48% | 300 ft |
| Napa County | 20,253 | 15% | 300 ft |
| Santa Clara County | 19,835 | 1% | 220 ft |
| Humboldt County | 18,043 | 13% | 96 ft |
| Siskiyou County | 17,918 | 41% | 145 ft |
| Amador County | 17,612 | 44% | 270 ft |
| Lake County | 16,448 | 24% | 115 ft |
| Sutter County | 16,157 | 16% | 100 ft |
| Solano County | 15,021 | 3% | 186 ft |
| Mariposa County | 12,168 | 71% | 225 ft |
| San Benito County | 11,560 | 18% | 225 ft |
| Lassen County | 11,208 | 34% | 150 ft |
| Marin County | 10,766 | 4% | 158 ft |
| Glenn County | 10,635 | 37% | 130 ft |
| Alameda County | 10,328 | under 1% | 220 ft |
| Plumas County | 8,733 | 44% | 146 ft |
| San Mateo County | 8,632 | 1% | 140 ft |
| Trinity County | 8,585 | 53% | 169 ft |
| Del Norte County | 8,487 | 31% | 41 ft |
| Ventura County | 7,880 | under 1% | 280 ft |
| Inyo County | 7,788 | 41% | 150 ft |
| Colusa County | 5,537 | 25% | 180 ft |
| Modoc County | 4,309 | 50% | 200 ft |
| Mono County | 3,360 | 25% | 200 ft |
| Sierra County | 1,151 | 36% | 165 ft |
| Alpine County | 837 | 70% | 250 ft |
| San Francisco County | 11 | under 1% | 150 ft |
Questions people ask about well water in California
Does California require private wells to be tested?
California doesn't require routine testing of existing private wells. Keeping a well safe is up to the owner, so test for bacteria and nitrate every year.
Where can I get my well water tested in California?
The State and Regional Water Boards fund or regulate 11 domestic well programs that offer free well testing in their service areas. Otherwise, use a lab certified by California for drinking water. The state's list is linked on this page.
Where these numbers come from
- How many people use wells: EPA estimates from the 2020 Census.
- Lab tests: Water Quality Portal (USGS and EPA), well samples since 2000.
- State programs and links: State Water Resources Control Board.