Manganese and arsenic are worth checking in Clark County wells.
2 worth checking, 4 rare out of 6 health checks.
From 18 wells tested in Clark County since 2000; your own well needs its own test. How to read this
Not charted, because fewer than 10 wells were tested: radon (6).
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 3 people 44,207 people
Nobody else tests these wells. Only you do.
People on wells: EPA researchers' 2020 estimate
How deep wells go here
Middle depth: some shelter from the surface, not complete.
Well depths: US Groundwater Well Database
Radon risk (a gas from rock)
Likely here. Test your home's air first.
Radon zones: EPA map
Here's how Clark County compares with Ohio and the counties around it.
Each result puts Clark County next to the 5 counties that border it, on the chart's 0 to 50% scale.
These 2 are worth checking in Clark County.
Manganese2 of 18 wells over
Too few tested to show: Madison.
Arsenic1 of 18 wells over
Too few tested to show: Madison.
These 4 are rare in Clark County.
Lead0 of 18 wells over
Too few tested to show: Madison.
Nitrate0 of 15 wells over
Too few tested to show: Madison.
Uranium0 of 14 wells over
Too few tested to show: Madison.
Fluoride0 of 18 wells over
Too few tested to show: Madison.
Too few Clark County wells were tested for this one.
Radon in water6 wells tested
Coliform bacteria turned up in 3 of 7 tested Clark County wells, so test for it every year.
Coliform bacteria3 of 7 wells had it
E. coli1 of 7 wells had it
E. coli means human or animal waste is getting in, so if a test of your Clark County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 8 of 18 tested wells, and it isn't a health risk.
Iron stains8 of 18 wells had it
Too few tested to show: Madison.
Clark County has 18 tested wells, and the busiest decade for testing was the 2010s.
Only 5 of the 18 wells have a test from 2020 or later, so a fresh test of your own well tells you more than any of these.
Most Clark 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 Clark County.
- Bacteria
- Nitrate
- Manganese
- Arsenic
What Ohio offers well owners
- Free testingWe didn't find a free program for all of Ohio. Ohio's private well page
- Certified labsOhio's list of certified labs
- Well recordsOhio's well record search
Half the household wells here are shallower than 82 feet.
That comes from 9,423 household wells in Ohio's drilling records. Most wells of every kind here are 54 to 121 feet deep. Wells as deep as Clark 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 are shallower than in 51 of the 87 other Ohio counties with enough drilling records.
Look up your own well's depth in Ohio'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 Clark County.
Clark 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 5 town water systems in Clark County test for PFAS. 1 found some PFAS, all below the new limits. Only 5 wells in Clark 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 Clark County
Is well water in Clark County safe to drink?
2 of 18 wells tested in Clark County had manganese over the limit, about 1 in 9. Across Ohio it's about 2 in 10. That's a bigger share than in 9 of the 14 other Ohio counties with 10 or more tested wells. So test your own well for manganese before you count on it.
Where can I get my well tested in Clark County?
Use a lab Ohio has certified for drinking water. Ohio's list is linked above, in the box about testing. Ask for bacteria, nitrate, manganese and arsenic, the tests that matter most in Clark County.
How deep are wells in Clark County?
Half the household wells here are shallower than 82 feet. Typical household wells here are shallower than in 51 of the 87 other Ohio counties with enough drilling records.
How does Clark County compare with the counties around it?
For manganese, the share of tested wells over the limit: No neighboring county with data had a higher share than Clark County, at 11%. Groundwater doesn't stop at county lines, so Greene's 11% is worth knowing about if you live near it.
How often should I test my well in Clark County?
In Clark County, 3 of 7 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 Clark County numbers come from
- People on wells: 44,207 in Clark County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 287 well water samples from 18 wells in the Water Quality Portal, run by the USGS and EPA, 2000 to 2020.
- Well depths: 9,423 Ohio drilling records for Clark County, gathered in the US Groundwater Well Database (Lin and others, 2024).
- Neighboring counties: the 5 counties that share a border with Clark County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 5 town water systems in Clark County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Clark County is zone 1 on the EPA Map of Radon Zones.
- State programs and links: Department of Health, checked November 1, 2026.