Well water in Carroll County, Maryland
1in5
Testing strongly recommended
tested well samples in Carroll County exceeded the EPA limit for nitrate (10 mg/L), based on public data from USGS Water Quality Portal.
1,261 test results across 13 contaminants from at least 176 wells, 1945 to 2020; nitrate has the most at 281. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
An estimated 72,149 people in Carroll County get their drinking water from a private well, per USGS 2015 county water use. That is about 43% of residents.
Separately, the USGS national arsenic model estimates that 2% of the 72,149 people on private wells in Carroll County draw water above 10 ug/L (the model's range is 1% to 3%), from geology and well depth rather than local tests.
What individual samples found
Each row summarizes every public sample for that contaminant inside Carroll County. Above limit means above the EPA maximum contaminant level; where EPA has no enforceable limit, the row shows a health guideline or nuisance level instead.
| Contaminant | Above limit | Samples | Detected | Median | Highest | Limit |
|---|---|---|---|---|---|---|
| Nitrate 1945 to 2019 | 281 | 99% | 4.8 | 110 | 10 mg/L EPA limit | |
| Lead 1986 to 2019 | 56 | 59% | 0.185 | 73 | 15 ug/L EPA limit | |
| Arsenic 1986 to 2019 | 53 | 21% | 0 | 10.1 | 10 ug/L EPA limit | |
| Fluoride 1945 to 2019 | 137 | 50% | 0.02 | 0.3 | 4 mg/L EPA limit | |
| Copper 1952 to 2019 | 58 | 91% | 0.011 | 0.1 | 1.3 mg/L EPA limit | |
| Radium (226 + 228) 1955 to 2014 | 13 | 15% | 0 | 1.4 | 5 pCi/L EPA limit | |
| Uranium 1955 to 2019 | 13 | 31% | 0 | 4 | 30 ug/L EPA limit | |
| Chloride 1945 to 2019 | no limit | 230 | 100% | 7.75 | 476 | 250 mg/L nuisance level |
| Sodium 1945 to 2019 | no limit | 138 | 100% | 7.22 | 98 | 20 mg/L health guideline |
| Iron 1945 to 2019 | no limit | 136 | 85% | 60 | 21,000 | 300 ug/L nuisance level |
| Manganese 1951 to 2019 | no limit | 131 | 71% | 20 | 1,950 | 300 ug/L health guideline |
| Radon 1992 to 2020 | no limit | 13 | 100% | 2,300 | 7,360 | 2,000 pCi/L health guideline |
Sampled fewer than 10 times, too few to summarize: E. coli (2).
Over time
Share of samples above the limit by period. A cell needs ten samples to show; a comparison needs twenty in each period. Later periods sample fewer wells, and often the ones already known to have a problem.
| Contaminant | before 2000 | 2000s | 2010s | 2020s |
|---|---|---|---|---|
| Nitrate | 18%255 samples | 25%16 samples | 60%10 samples | n/a |
Closer than the county
See the sampled wells near your address
The same records, drawn around one point: which wells within a few miles were sampled and what they found, how deep the wells next to you were drilled, and any leaking tank or cleanup site within a mile.
Check my addressWhat this means
The contaminants most often above their limit here are nitrate (20% of 281 samples), lead (5% of 56 samples), and arsenic (2% of 53 samples). A well next door can differ sharply from yours because bedrock fractures, well depth and plumbing all matter, so these rates describe the area, not your tap.
Chloride, Iron, and Manganese are widespread in local groundwater. They are mainly a staining and taste problem, but high manganese also carries a health advisory for infants.
The median radon reading (2,300 pCi/L) is above the 2,000 pCi/L level at which treatment is recommended. Radon in water raises indoor air radon when it is used for showers and laundry.
What to test for in Carroll County
- 1Nitrate20% of 281 local samples were above the limit.
- 2Lead5% of 56 local samples were above the limit.
- 3Arsenic2% of 53 local samples were above the limit.
- 4Coliform bacteriaRecommended for every private well, every year.
- 5RadonMedian local reading is 2,300 pCi/L.
- 6ChlorideDetected in 100% of local samples.
- 7CopperDetected in 91% of local samples.
Test your Carroll County well for nitrate, lead and arsenic
Certified lab analysis of your own tap water, bottles and prepaid return shipping included. The Essential well panel covers arsenic, uranium, nitrate, lead, copper, manganese, iron, sodium and bacteria; radon and PFAS are add-ons.
Order the Tap Score well water test kit, from $209Already tested? Upload the report
Just want bacteria checked first? Tap Score coliform and E. coli test, $99. Coliform and E. coli are the tests every well needs every year.
Want a quick look before paying for a lab? Home well water test strips on Amazon check hardness, iron, pH and nitrate in minutes. They are a screen, not a result: arsenic, bacteria, uranium and PFAS need a certified lab.
Affiliate links: the merchant pays us a commission and the price is the same for you. It does not change what the data above says. As an Amazon Associate we earn from qualifying purchases.
Where to get a well tested in Maryland: certified labs, state programs and prices.
Already have results back? Get your lab report read against the Carroll County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
The rock under Carroll County
Piedmont and Blue Ridge crystalline-rock aquifers
Igneous and metamorphic-rock. Granite and similar crystalline rock hold water only in fractures. Wells are deep and yields modest, and the rock itself is the source of arsenic, radon and uranium, which is why those three head the test list in bedrock country.
Classification from the USGS Principal Aquifers of the United States (national map, 2003 edition, GIS release 2015), read at the county centroid. A single well can sit in a different unit, especially near a boundary.
Official help in Maryland
Two places to start that are not selling anything: the state program that answers private well questions, and its list of labs certified to run drinking water tests. A certified lab is the difference between a result you can act on and a number.
Contamination sources on record in Carroll County
MDE Land Restoration Program sites records 53 regulated sites in Carroll County, among 53 regulated sites in total. Groundwater does not follow property lines, so a well within a few hundred feet of one of these is worth testing for what that site could release.
- 53
- other remediation projects
Treatment that fits the local profile
Nitrate
Point-of-use reverse osmosis; Anion exchange; Distillation
Lead
Point-of-use reverse osmosis; Certified lead-removal carbon filter; Neutralizing filter to raise pH and stop leaching
Arsenic
Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
Radon
Aeration (bubble-up or diffused) whole-house; Granular activated carbon whole-house (lower levels only)
Iron
Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration
Systems we would look at first
Some links below are affiliate links. If you buy through one, the merchant pays us a commission at no extra cost to you. It does not change which products we list or what the data says.
For nitrate
Under-sink reverse osmosis system
under-sink or countertop, about $300
Look for NSF/ANSI 58 certification listing the contaminant you need removed.
For nitrate
Aquasana SmartFlow reverse osmosis
under-sink or countertop, about $225
Certified to NSF/ANSI 58 and 53 to reduce arsenic (96%, pentavalent), fluoride (90%), lead (99%), nitrate, nitrite and PFOA/PFOS at the kitchen tap, with a remineralizer.
For lead
Aquasana Claryum 3-Stage under-sink filter
under-sink or countertop, about $175
Certified to NSF/ANSI 53 to reduce 99% of lead and 99.7% of PFOA and PFOS at the tap. Not a fix for arsenic, nitrate or bacteria.
For lead
Acid neutralizing filter
whole-house, at the point of entry, about $1,200
Raises pH so plumbing stops leaching lead and copper.
For arsenic
Whole-house arsenic and uranium filter
whole-house, at the point of entry, about $2,500
Adsorptive iron-based media; sized to your well yield.
For iron
Iron and manganese oxidizing filter
whole-house, at the point of entry, about $1,800
Air-injection or greensand media; fixes staining at the source.
Free, no obligation
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Common questions
Is there arsenic in well water in Carroll County?
Arsenic was detected in 21% of 53 public well samples in Carroll County, and 2% were above the EPA limit of 10 ug/L. Arsenic has no taste or smell; a lab test is the only way to know your level.
How high is radon in well water in Carroll County?
The median radon level across 13 public samples in Carroll County was 2,300 pCi/L, with a high of 7,360 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Carroll County?
Test for bacteria and nitrate every year. Test once for arsenic, uranium, radon, fluoride, manganese and PFAS, then again every three to five years or after any change in taste, color, or plumbing.
Counties near Carroll County
Closest first. Groundwater does not stop at a line on a map, so the next county over is a fair second opinion.
Want the numbers themselves? Download the Maryland dataset as CSV, every county and town, with the sources named.
Sources
- USGS Water Quality Portal: 1,261 samples in Carroll County. Data from the Water Quality Portal, a service of USGS, EPA and USDA; groundwater samples collected by USGS and cooperators. Retrieved September 3, 2026.
- USGS national arsenic model (Ayotte 2017): estimated share of 72,149 people on private wells in Carroll County above 10 ug/L of arsenic, from geology, well depth and land use. County estimates of domestic well users with arsenic above 10 ug/L from the USGS national logistic regression model (Ayotte, Medalie and Qi, 2017), with private well population from the USGS 2015 county water-use compilation (Dieter and others, 2018). Retrieved September 15, 2026.
- MDE Land Restoration Program sites: 53 regulated sites located in Carroll County. Brownfield, voluntary cleanup and Superfund sites from the Maryland Department of the Environment Land Restoration Program. Retrieved September 18, 2026.
Non-detects count as samples and are treated as zero when computing medians. Exactly at the limit counts as not above it. A sample belongs to the town containing the well's reported coordinates.