Radon is widespread in Chester County wells.
1 widespread, 1 worth checking, 5 rare out of 7 health checks.
From 186 wells tested in Chester 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
1 in 5 people 117,808 people
Nobody else tests these wells. Only you do.
People on wells: EPA researchers' 2020 estimate
Radon risk (a gas from rock)
Likely here. Test your home's air first.
Radon zones: EPA map
Here's how Chester County compares with Pennsylvania and the counties around it.
Each result puts Chester County next to the 6 counties that border it, on the chart's 0 to 50% scale.
This one is widespread in Chester County wells.
Radon in water20 of 71 wells over
Too few tested to show: Cecil, MD, Delaware, Montgomery.
This one is worth checking in Chester County.
Nitrate23 of 168 wells over
* Likely overstated, so we don't rank it.
Too few tested to show: Delaware.
These 5 are rare in Chester County.
Lead1 of 89 wells over
Too few tested to show: Delaware, New Castle, DE.
Manganese1 of 131 wells over
* Likely overstated, so we don't rank it.
Too few tested to show: Delaware.
Arsenic0 of 125 wells over
Too few tested to show: Delaware.
Fluoride0 of 131 wells over
Too few tested to show: Delaware.
Uranium0 of 41 wells over
Too few tested to show: Delaware, New Castle, DE.
Coliform bacteria turned up in 7 of 19 tested Chester County wells, so test for it every year.
Coliform bacteria7 of 19 wells had it
Too few tested to show: Cecil, MD, Delaware, New Castle, DE.
E. coli1 of 15 wells had it
Too few tested to show: Cecil, MD, Delaware, New Castle, DE.
E. coli means human or animal waste is getting in, so if a test of your Chester County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 10 of 131 tested wells, and it isn't a health risk.
Iron stains10 of 131 wells had it
Too few tested to show: Delaware.
Most of the 186 wells tested in Chester County were last tested before 2010.
An old result shows the water as it was then, so treat these 186 wells as a starting point and test your own.
Most Chester 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 Chester County.
- Bacteria
- Nitrate
- Radon in water
- Arsenic
What Pennsylvania offers well owners
- Free testingWe didn't find a free program for all of Pennsylvania. Pennsylvania's private well page
- Certified labsPennsylvania's list of certified labs
- Well recordsPennsylvania's well record search
Here's what we know about radon and PFAS in Chester County.
Chester County is in the EPA's highest radon zone. Radon from well water adds to the radon in your indoor air, so test your air first, and your water too if the air is high. Radon guide
Between 2023 and 2025 the EPA had 11 town water systems in Chester County test for PFAS. 9 of them had at least one test above 4 ng/L, the new EPA limit for PFOA and PFOS. The highest single result was 18 ng/L of PFOA. No well in Chester County has 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 Chester County
Is well water in Chester County safe to drink?
20 of 71 wells tested in Chester County had radon in water over the limit, about 3 in 10. Across Pennsylvania it's about 1 in 15. That's the highest share among the 18 Pennsylvania counties with 10 or more tested wells. So test your own well for radon in water before you count on it.
Where can I get my well tested in Chester County?
Use a lab Pennsylvania has certified for drinking water. Pennsylvania's list is linked above, in the box about testing. Ask for bacteria, nitrate, radon in water and arsenic, the tests that matter most in Chester County.
How does Chester County compare with the counties around it?
For radon in water, the share of tested wells over the limit: Chester County, at 28%, had a higher share than all 3 neighboring counties with data. Groundwater doesn't stop at county lines, so Lancaster's 9% is worth knowing about if you live near it.
How often should I test my well in Chester County?
In Chester County, 7 of 19 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 Chester County numbers come from
- People on wells: 117,808 in Chester County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 1,884 well water samples from 186 wells in the Water Quality Portal, run by the USGS and EPA, 2000 to 2023.
- Neighboring counties: the 6 counties that share a border with Chester County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 11 town water systems in Chester County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Chester County is zone 1 on the EPA Map of Radon Zones.
- State programs and links: Department of Environmental Protection, checked November 1, 2026.