Nitrate and manganese are widespread in Carroll County wells.
2 widespread, 1 worth checking, 2 rare out of 5 health checks.
From 12 wells tested in Carroll County since 2001; your own well needs its own test. How to read this
Not charted, because fewer than 10 wells were tested: uranium (6), 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
5 in 10 people 89,105 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)
Likely here. Test your home's air first.
Radon zones: EPA map
Here's how Carroll County compares with Maryland and the counties around it.
Each result puts Carroll County next to the 5 counties that border it, on the chart's 0 to 50% scale.
These 2 are widespread in Carroll County wells.
Nitrate2 of 10 wells over
Too few tested to show: Howard.
Manganese2 of 11 wells over
Too few tested to show: Adams, PA, Howard, York, PA.
This one is worth checking in Carroll County.
Arsenic1 of 11 wells over
Too few tested to show: Adams, PA, Baltimore, Howard.
These 2 are rare in Carroll County.
Lead0 of 11 wells over
Too few tested to show: Adams, PA, Howard, York, PA.
Too few Carroll County wells were tested for these 2.
Uranium6 wells tested
Radon in water6 wells tested
Coliform bacteria turned up in 1 of 2 tested Carroll County wells, so test for it every year.
Coliform bacteria1 of 2 wells had it
E. coli0 of 2 wells had it
E. coli means human or animal waste is getting in, so if a test of your Carroll County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 2 of 11 tested wells, and it isn't a health risk.
Iron stains2 of 11 wells had it
Too few tested to show: Adams, PA, Howard, York, PA.
Most of the 12 wells tested in Carroll County were last tested before 2010.
An old result shows the water as it was then, so treat these 12 wells as a starting point and test your own.
Most Carroll 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 Carroll County.
- Bacteria
- Nitrate
- Manganese
- Arsenic
What Maryland offers well owners
- Free testingWe didn't find a free program for all of Maryland. Maryland's private well page
- Certified labsMaryland's list of certified labs
- Well recordsWe didn't find an online search.
- New wellsSince October 1, 2024, Md. Code, Real Property 10-713 requires a contract for sale of property with a private well to make well water quality testing a condition of sale, with both parties certifying they reviewed the results.
Half the household wells here are shallower than 150 feet.
That comes from 31,814 household wells in Maryland's drilling records. Most wells of every kind here are 100 to 230 feet deep. Wells as deep as Carroll 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 15 of the 23 other Maryland counties with enough drilling records.
How to find your own well's depth
Well depths: US Groundwater Well Database
Here's what we know about radon and PFAS in Carroll County.
Carroll 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 6 town water systems in Carroll County test for PFAS. 5 of them had at least one test above 4 ng/L, the new EPA limit for PFOA and PFOS. The highest single result was 13 ng/L of PFOA. No well in Carroll 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 Carroll County
Is well water in Carroll County safe to drink?
2 of 10 wells tested in Carroll County had nitrate over the limit, about 2 in 10. Across Maryland it's about 1 in 10. That's a bigger share than in 16 of the 17 other Maryland counties with 10 or more tested wells, leaving out 1 county whose results are likely overstated. So test your own well for nitrate before you count on it.
Where can I get my well tested in Carroll County?
Use a lab Maryland has certified for drinking water. Maryland's list is linked above, in the box about testing. Ask for bacteria, nitrate, manganese and arsenic, the tests that matter most in Carroll County.
How deep are wells in Carroll County?
Half the household wells here are shallower than 150 feet. Typical household wells here are shallower than in 15 of the 23 other Maryland counties with enough drilling records.
How does Carroll County compare with the counties around it?
For nitrate, the share of tested wells over the limit: Carroll County, at 20%, had a higher share than all 4 neighboring counties with data. Groundwater doesn't stop at county lines, so York, PA's 12% is worth knowing about if you live near it.
How often should I test my well in Carroll County?
In Carroll County, 1 of 2 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 Carroll County numbers come from
- People on wells: 89,105 in Carroll County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 109 well water samples from 12 wells in the Water Quality Portal, run by the USGS and EPA, 2001 to 2020.
- Well depths: 31,814 Maryland drilling records for Carroll County, gathered in the US Groundwater Well Database (Lin and others, 2024).
- Neighboring counties: the 5 counties that share a border with Carroll County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 6 town water systems in Carroll County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Carroll County is zone 1 on the EPA Map of Radon Zones.
- State programs and links: Maryland Department of the Environment, checked November 1, 2026.