Manganese and uranium are widespread in San Diego County wells.
2 widespread, 3 worth checking, 2 rare out of 7 health checks.
From 229 wells tested in San Diego County since 2002; 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 36 people 90,496 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 San Diego County compares with California and the counties around it.
Each result puts San Diego County next to the 3 counties that border it, on the chart's 0 to 50% scale.
These 2 are widespread in San Diego County wells.
Manganese45 of 203 wells over
Uranium14 of 70 wells over
These 3 are worth checking in San Diego County.
Arsenic25 of 207 wells over
Radon in water8 of 70 wells over
Too few tested to show: Imperial.
Nitrate14 of 212 wells over
These 2 are rare in San Diego County.
Lead1 of 70 wells over
None of the 8 San Diego County wells tested for bacteria had it, but every well needs a yearly test.
Coliform bacteria0 of 8 wells had it
E. coli8 of 17 wells had it
Too few tested to show: Imperial.
E. coli means human or animal waste is getting in, so if a test of your San Diego County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 55 of 209 tested wells, and it isn't a health risk.
Iron stains55 of 209 wells had it
San Diego County has 229 tested wells, and the busiest decade for testing was the 2010s.
Only 18 of the 229 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 Diego 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 Diego County.
- Bacteria
- Nitrate
- Manganese
- Uranium
- Arsenic
- Radon in water
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 340 feet.
That comes from 9,331 household wells in California's drilling records. Most wells of every kind here are 150 to 570 feet deep. Wells as deep as San Diego 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 54 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 Diego County.
San Diego 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 27 town water systems in San Diego County test for PFAS. 4 of them had at least one test above 4 ng/L, the new EPA limit for PFOA and PFOS. The highest single result was 188 ng/L of PFOA. Only 9 wells in San Diego 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 Diego County
Is well water in San Diego County safe to drink?
45 of 203 wells tested in San Diego County had manganese over the limit, about 2 in 10. Across California it's about 1 in 12. That's a bigger share than in 40 of the 45 other California counties with 10 or more tested wells. So test your own well for manganese before you count on it.
Can I get my well tested for free in San Diego 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, manganese, uranium, arsenic and radon in water, the tests that matter most in San Diego County.
How deep are wells in San Diego County?
Half the household wells here are shallower than 340 feet. Typical household wells here go deeper than in 54 of the 56 other California counties with enough drilling records.
How does San Diego County compare with the counties around it?
For manganese, the share of tested wells over the limit: San Diego County, at 22%, had a higher share than all 3 neighboring counties with data. Groundwater doesn't stop at county lines, so Orange's 21% is worth knowing about if you live near it.
How often should I test my well in San Diego County?
None of the 8 wells tested for bacteria in San Diego 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 San Diego County numbers come from
- People on wells: 90,496 in San Diego County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 2,084 well water samples from 229 wells in the Water Quality Portal, run by the USGS and EPA, 2002 to 2024.
- Well depths: 9,331 California drilling records for San Diego County, gathered in the US Groundwater Well Database (Lin and others, 2024).
- Neighboring counties: the 3 counties that share a border with San Diego County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 27 town water systems in San Diego County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: San Diego County is zone 3 on the EPA Map of Radon Zones.
- State programs and links: State Water Resources Control Board, checked November 1, 2026.