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Lead in California well water, by county

By the Tested Water teamLab data from the USGS and EPA Water Quality Portal, 2000 to 2026Updated November 8, 2026

Lead is worth checking in 1 of the 43 California counties with 10 or more tested wells, and rare in the rest. A county's share tells you how likely a problem is nearby. Only a test of your own well tells you what's in it.

Find a lead test See every county

These tests sample the groundwater, and lead rarely comes from the ground. In a home it mostly comes from plumbing: old solder, brass fittings and some older pumps. So a county's share can't tell you about your pipes. Test a first-draw sample, water that sat in the pipes overnight, from the tap you drink from.

How California compares with the rest of the country

Across California, under 1 in 50 tested wells had lead over the EPA action level of 15 µg/L (12 of 2,851). Across all tested wells in the US it's under 1 in 50. That's less often than in the country as a whole. Counties still differ, so check yours below.

Why it matters: It harms children's growing brains. The CDC says no amount in a child's blood is known to be safe.

Lead in tested wells, county by county

Share of each county's tested wells with at least one result over the EPA action level of 15 µg/L. Counties need 10 or more tested wells to be listed. Widespread means 15% or more, worth checking 5 to 15%, rare under 5%.

CountyWells testedWells over the limitLevel
Lake County 13
8% 1 of 13
 Worth checking
Napa County 23
4% 1 of 23
 Rare
Riverside County 223
4% 8 of 223
 Rare
San Diego County 70
1% 1 of 70
 Rare
Stanislaus County 131
1% 1 of 131
 Rare
San Bernardino County 572
0% 0 of 572
 Rare
Kern County 171
0% 0 of 171
 Rare
Los Angeles County 153
0% 0 of 153
 Rare
Fresno County 112
0% 0 of 112
 Rare
Santa Barbara County 92
0% 0 of 92
 Rare
Sonoma County 83
0% 0 of 83
 Rare
Monterey County 71
0% 0 of 71
 Rare
Merced County 69
0% 0 of 69
 Rare
Sacramento County 66
0% 0 of 66
 Rare
Madera County 64
0% 0 of 64
 Rare
Tulare County 59
0% 0 of 59
 Rare
San Joaquin County 57
0% 0 of 57
 Rare
Alameda County 56
0% 0 of 56
 Rare
Santa Clara County 55
0% 0 of 55
 Rare
Orange County 52
0% 0 of 52
 Rare
El Dorado County 45
0% 0 of 45
 Rare
Ventura County 44
0% 0 of 44
 Rare
Tehama County 43
0% 0 of 43
 Rare
San Luis Obispo County 40
0% 0 of 40
 Rare
Butte County 39
0% 0 of 39
 Rare
Santa Cruz County 38
0% 0 of 38
 Rare
Nevada County 37
0% 0 of 37
 Rare
Shasta County 32
0% 0 of 32
 Rare
San Benito County 28
0% 0 of 28
 Rare
Imperial County 27
0% 0 of 27
 Rare
Mendocino County 27
0% 0 of 27
 Rare
Placer County 23
0% 0 of 23
 Rare
Kings County 22
0% 0 of 22
 Rare
Inyo County 20
0% 0 of 20
 Rare
Humboldt County 19
0% 0 of 19
 Rare
Glenn County 16
0% 0 of 16
 Rare
Mono County 15
0% 0 of 15
 Rare
Siskiyou County 14
0% 0 of 14
 Rare
Sutter County 14
0% 0 of 14
 Rare
San Mateo County 12
0% 0 of 12
 Rare
Yolo County 12
0% 0 of 12
 Rare
Amador County 11
0% 0 of 11
 Rare
Modoc County 10
0% 0 of 10
 Rare

13 more California counties have 1 to 9 tested wells for lead, too few to rate.

Download this table (CSV) · Free to reuse under CC BY 4.0

Where to get your well tested for lead in California

1

Free testing, with limits

Free testing in California depends on where you live: 11 local domestic well programs offer it in their areas. Check which tests it includes before you count on it for lead.

California's private well page
3

A mail-in kit

Fill the bottles at your kitchen tap and mail them back. We mark the kits that include lead.

Compare kits

Keep reading about wells in California

Questions people ask about lead in California

Is there lead in California well water?

Lead is worth checking in 1 of the 43 California counties with 10 or more tested wells, and rare in the rest. Across California, under 1 in 50 tested wells had lead over the EPA action level of 15 µg/L (12 of 2,851). Across all tested wells in the US it's under 1 in 50. That's less often than in the country as a whole. Counties still differ, so check yours below.

Where can I get my well tested for lead in California?

Free testing in California depends on where you live: 11 local domestic well programs offer it in their areas. If that doesn't cover you, use a lab certified by California for drinking water, or a mail-in kit that includes lead from a certified lab.

See California's list of certified labs, or compare mail-in kits.

Where these numbers come from

  • Lab tests: Water Quality Portal (USGS and EPA), well samples since 2000. A well counts as over if any of its tests was over the EPA action level of 15 µg/L. Wells tested for studies and monitoring, not a random sample of homes.
  • Likely overstated: our own check of who tested the wells, when and where. How we check.
  • State programs and links: State Water Resources Control Board.