Uranium and manganese are widespread in Orange County wells.
2 widespread, 2 worth checking, 3 rare out of 7 health checks.
From 80 wells tested in Orange 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 70 people 45,836 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)
Less likely, but the EPA still says test your air.
Radon zones: EPA map
Here's how Orange County compares with California and the counties around it.
Each result puts Orange County next to the 4 counties that border it, on the chart's 0 to 50% scale.
These 2 are widespread in Orange County wells.
Uranium12 of 52 wells over
Manganese17 of 80 wells over
These 2 are worth checking in Orange County.
Arsenic5 of 60 wells over
Nitrate5 of 79 wells over
These 3 are rare in Orange County.
Fluoride2 of 80 wells over
Radon in water0 of 36 wells over
Lead0 of 52 wells over
None of the 21 Orange County wells tested for bacteria had it, but every well needs a yearly test.
Coliform bacteria0 of 21 wells had it
Too few tested to show: San Diego.
E. coli0 of 21 wells had it
E. coli means human or animal waste is getting in, so if a test of your Orange County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 11 of 80 tested wells, and it isn't a health risk.
Iron stains11 of 80 wells had it
Most of the 80 wells tested in Orange County were last tested before 2010.
An old result shows the water as it was then, so treat these 80 wells as a starting point and test your own.
Most Orange 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 5 things to check in Orange County.
- Bacteria
- Nitrate
- Uranium
- Manganese
- Arsenic
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 204 feet.
That comes from 550 household wells in California's drilling records. Most wells of every kind here are 40 to 420 feet deep. Wells as deep as Orange 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 30 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 Orange County.
Orange County is in the EPA's lowest radon zone, so radon from well water is unlikely to be a problem. Radon guide
Between 2023 and 2025 the EPA had 30 town water systems in Orange County test for PFAS. 11 of them had at least one test above 4 ng/L, the new EPA limit for PFOA and PFOS. The highest single result was 29 ng/L of PFOS. Only 7 wells in Orange 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 Orange County
Is well water in Orange County safe to drink?
12 of 52 wells tested in Orange County had uranium over the limit, about 1 in 4. Across California it's about 1 in 13. That's a bigger share than in 41 of the 43 other California counties with 10 or more tested wells. So test your own well for uranium before you count on it.
Can I get my well tested for free in Orange 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, uranium, manganese and arsenic, the tests that matter most in Orange County.
How deep are wells in Orange County?
Half the household wells here are shallower than 204 feet. Typical household wells here go deeper than in 30 of the 56 other California counties with enough drilling records.
How does Orange County compare with the counties around it?
For uranium, the share of tested wells over the limit: Orange County, at 23%, had a higher share than all 4 neighboring counties with data. Groundwater doesn't stop at county lines, so San Diego's 20% is worth knowing about if you live near it.
How often should I test my well in Orange County?
None of the 21 wells tested for bacteria in Orange County had it, but the CDC still says to 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 Orange County numbers come from
- People on wells: 45,836 in Orange County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 892 well water samples from 80 wells in the Water Quality Portal, run by the USGS and EPA, 2000 to 2020.
- Well depths: 550 California drilling records for Orange County, gathered in the US Groundwater Well Database (Lin and others, 2024).
- Neighboring counties: the 4 counties that share a border with Orange County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 30 town water systems in Orange County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Orange County is zone 3 on the EPA Map of Radon Zones.
- State programs and links: State Water Resources Control Board, checked November 1, 2026.