Arsenic is widespread in San Bernardino County wells.
1 widespread, 4 worth checking, 2 rare out of 7 health checks.
From 1,009 wells tested in San Bernardino 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 27 people 80,772 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 San Bernardino County compares with California and the counties around it.
Each result puts San Bernardino County next to the 8 counties that border it, on the chart's 0 to 50% scale.
This one is widespread in San Bernardino County wells.
Arsenic241 of 984 wells over
These 4 are worth checking in San Bernardino County.
Uranium59 of 569 wells over
Too few tested to show: La Paz, AZ.
Radon in water8 of 83 wells over
Too few tested to show: Clark, NV, Inyo.
Nitrate88 of 984 wells over
Fluoride83 of 982 wells over
These 2 are rare in San Bernardino County.
Manganese26 of 977 wells over
Lead0 of 572 wells over
Coliform bacteria turned up in 11 of 75 tested San Bernardino County wells, so test for it every year.
Coliform bacteria11 of 75 wells had it
Too few tested to show: Clark, NV, Inyo, La Paz, AZ, Mohave, AZ.
E. coli1 of 75 wells had it
Too few tested to show: Clark, NV, Inyo, La Paz, AZ, Mohave, AZ.
E. coli means human or animal waste is getting in, so if a test of your San Bernardino County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 55 of 983 tested wells, and it isn't a health risk.
Iron stains55 of 983 wells had it
San Bernardino County has 1,009 tested wells, and the busiest decade for testing was the 2010s.
Only 114 of the 1,009 wells have a test from 2020 or later, so a fresh test of your own well tells you more than any of these.
Most San Bernardino 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 6 things to check in San Bernardino County.
- Bacteria
- Nitrate
- Arsenic
- Uranium
- Radon in water
- Fluoride
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 250 feet.
That comes from 11,150 household wells in California's drilling records. Most wells of every kind here are 170 to 400 feet deep. Wells as deep as San Bernardino 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 40 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 San Bernardino County.
San Bernardino 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 49 town water systems in San Bernardino County test for PFAS. 18 of them had at least one test above 4 ng/L, the new EPA limit for PFOA and PFOS. The highest single result was 236 ng/L of PFOS. Only 38 wells in San Bernardino 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 San Bernardino County
Is well water in San Bernardino County safe to drink?
241 of 984 wells tested in San Bernardino County had arsenic over the limit, about 1 in 4. Across California it's about 1 in 7. That's a bigger share than in 40 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 San Bernardino 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, uranium, radon in water and fluoride, the tests that matter most in San Bernardino County.
How deep are wells in San Bernardino County?
Half the household wells here are shallower than 250 feet. Typical household wells here go deeper than in 40 of the 56 other California counties with enough drilling records.
How does San Bernardino County compare with the counties around it?
For arsenic, the share of tested wells over the limit: 3 of the 8 neighboring counties with data had a higher share than San Bernardino County, at 24%. La Paz, AZ had the most, at 29%. Groundwater doesn't stop at county lines, so La Paz, AZ's 29% is worth knowing about if you live near it.
How often should I test my well in San Bernardino County?
In San Bernardino County, 11 of 75 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 San Bernardino County numbers come from
- People on wells: 80,772 in San Bernardino County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 16,327 well water samples from 1,009 wells in the Water Quality Portal, run by the USGS and EPA, 2000 to 2023.
- Well depths: 11,150 California drilling records for San Bernardino County, gathered in the US Groundwater Well Database (Lin and others, 2024).
- Neighboring counties: the 8 counties that share a border with San Bernardino County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 49 town water systems in San Bernardino County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: San Bernardino County is zone 2 on the EPA Map of Radon Zones.
- State programs and links: State Water Resources Control Board, checked November 1, 2026.