Arsenic and manganese are worth checking in Los Angeles County wells.
2 worth checking, 5 rare out of 7 health checks.
From 486 wells tested in Los Angeles County since 2000; your own well needs its own test. How to read this
Rare: under 5%Worth checking: 5 to 15%Widespread: 15%+
Lab results: Water Quality Portal (USGS and EPA)
Who drinks from a well here
About 1 in 88 people 113,474 people
Nobody else tests these wells. Only you do.
People on wells: EPA researchers' 2020 estimate
How deep wells go here
Deep wells: fewer surface germs, more minerals from the rock.
Well depths: US Groundwater Well Database
Radon risk (a gas from rock)
Possible here. A home air test is inexpensive.
Radon zones: EPA map
Here's how Los Angeles County compares with California and the counties around it.
Each result puts Los Angeles County next to the 4 counties that border it, on the chart's 0 to 50% scale.
These 2 are worth checking in Los Angeles County.
Arsenic59 of 472 wells over
Manganese24 of 470 wells over
These 5 are rare in Los Angeles County.
Nitrate14 of 438 wells over
Fluoride3 of 478 wells over
Uranium0 of 180 wells over
Radon in water0 of 77 wells over
Too few tested to show: Ventura.
Lead0 of 153 wells over
Coliform bacteria turned up in 14 of 43 tested Los Angeles County wells, so test for it every year.
Coliform bacteria14 of 43 wells had it
Too few tested to show: Ventura.
E. coli2 of 43 wells had it
Too few tested to show: Ventura.
E. coli means human or animal waste is getting in, so if a test of your Los Angeles County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 36 of 478 tested wells, and it isn't a health risk.
Iron stains36 of 478 wells had it
Los Angeles County has 486 tested wells, and the busiest decade for testing was the 2000s.
Only 79 of the 486 wells have a test from 2020 or later, so a fresh test of your own well tells you more than any of these.
Most Los Angeles County wells in these records were tested for research or because someone suspected a problem, which can push the shares above what a typical home well would show (how we read the numbers).
One mail-in lab test covers the 4 things to check in Los Angeles County.
- Bacteria
- Nitrate
- Arsenic
- Manganese
What California offers well owners
- Free testingThe State and Regional Water Boards fund or regulate 11 domestic well programs that offer free well testing in their service areas. See the program
- Certified labsCalifornia's list of certified labs
- Well recordsCalifornia's well record search
Half the household wells here are shallower than 320 feet.
That comes from 4,484 household wells in California's drilling records. Most wells of every kind here are 81 to 450 feet deep. Wells as deep as Los Angeles County's are usually better protected from fertilizer and bacteria at the surface, but they can pick up more of what's in the rock, like arsenic and uranium. Typical household wells here go deeper than in 51 of the 56 other California counties with enough drilling records.
Look up your own well's depth in California's well record search, or see how to find it.
Well depths: US Groundwater Well Database
Here's what we know about radon and PFAS in Los Angeles County.
Los Angeles County is in the EPA's middle radon zone. An indoor air test is cheap and tells you whether to look at your water. Radon guide
Between 2023 and 2025 the EPA had 125 town water systems in Los Angeles County test for PFAS. 54 of them had at least one test above 4 ng/L, the new EPA limit for PFOA and PFOS. The highest single result was 59 ng/L of PFOS. Only 25 wells in Los Angeles County have public PFAS results, so the town systems are the best clue to what's in the groundwater nearby. PFAS guide
Radon zones: EPA Map of Radon Zones. PFAS: EPA tests of town water systems, 2023 to 2025
Questions people ask about well water in Los Angeles County
Is well water in Los Angeles County safe to drink?
59 of 472 wells tested in Los Angeles County had arsenic over the limit, about 1 in 8. Across California it's about 1 in 7. That's a bigger share than in 34 of the 46 other California counties with 10 or more tested wells. So test your own well for arsenic before you count on it.
Can I get my well tested for free in Los Angeles County?
The State and Regional Water Boards fund or regulate 11 domestic well programs that offer free well testing in their service areas. If not, use a lab California has certified for drinking water. Ask for bacteria, nitrate, arsenic and manganese, the tests that matter most in Los Angeles County.
How deep are wells in Los Angeles County?
Half the household wells here are shallower than 320 feet. Typical household wells here go deeper than in 51 of the 56 other California counties with enough drilling records.
How does Los Angeles County compare with the counties around it?
For arsenic, the share of tested wells over the limit: 2 of the 4 neighboring counties with data had a higher share than Los Angeles County, at 12%. Kern had the most, at 25%. Groundwater doesn't stop at county lines, so Kern's 25% is worth knowing about if you live near it.
How often should I test my well in Los Angeles County?
In Los Angeles County, 14 of 43 tested wells had coliform bacteria, so the CDC's advice matters here: test for bacteria and nitrate every year, and right away after a flood, a repair, or any change in taste or smell.
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Where the Los Angeles County numbers come from
- People on wells: 113,474 in Los Angeles County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 4,362 well water samples from 486 wells in the Water Quality Portal, run by the USGS and EPA, 2000 to 2023.
- Well depths: 4,484 California drilling records for Los Angeles County, gathered in the US Groundwater Well Database (Lin and others, 2024).
- Neighboring counties: the 4 counties that share a border with Los Angeles County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 125 town water systems in Los Angeles County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Los Angeles County is zone 2 on the EPA Map of Radon Zones.
- State programs and links: State Water Resources Control Board, checked November 1, 2026.