Well water in Baltimore County, Maryland
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Testing recommended
tested well samples in Baltimore County exceeded the EPA limit for nitrate (10 mg/L), based on public data from USGS Water Quality Portal.
4,949 test results across 13 contaminants from at least 344 wells, 1943 to 2020; nitrate has the most at 1,368. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
An estimated 131,371 people in Baltimore County get their drinking water from a private well, per USGS 2015 county water use. That is about 16% of residents.
Separately, the USGS national arsenic model estimates that 3% of the 131,371 people on private wells in Baltimore County draw water above 10 ug/L (the model's range is 2% to 5%), from geology and well depth rather than local tests.
What individual samples found
Each row summarizes every public sample for that contaminant inside Baltimore 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 1943 to 2019 | 1,368 | 96% | 1.69 | 70.8 | 10 mg/L EPA limit | |
| Radium (226 + 228) 1997 to 2003 | 13 | 62% | 1 | 18.6 | 5 pCi/L EPA limit | |
| Lead 1981 to 2019 | 187 | 64% | 0.44 | 70 | 15 ug/L EPA limit | |
| Fluoride 1943 to 2019 | 438 | 43% | 0 | 0.6 | 4 mg/L EPA limit | |
| Copper 1953 to 2019 | 152 | 89% | 0.01 | 0.56 | 1.3 mg/L EPA limit | |
| Arsenic 1981 to 2019 | 138 | 9% | 0 | 3 | 10 ug/L EPA limit | |
| Chloride 1943 to 2019 | no limit | 734 | 100% | 49 | 791 | 250 mg/L nuisance level |
| Iron 1943 to 2019 | no limit | 639 | 66% | 30 | 380,000 | 300 ug/L nuisance level |
| Sodium 1943 to 2019 | no limit | 571 | 100% | 13.6 | 409 | 20 mg/L health guideline |
| Manganese 1951 to 2019 | no limit | 519 | 72% | 10 | 5,000 | 300 ug/L health guideline |
| Radon 1994 to 2020 | no limit | 180 | 99% | 2,445 | 28,600 | 2,000 pCi/L health guideline |
Sampled fewer than 10 times, too few to summarize: Uranium (9), E. coli (1).
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 | 13%521 samples | 7%841 samples | n/a | n/a |
| Fluoride | 0%189 samples | 0%246 samples | n/a | n/a |
| Lead | 2%129 samples | 4%53 samples | n/a | n/a |
Nitrate above the limit in Baltimore County fell from 13% of 521 samples before 2000 to 7% of 841 in the 2000s.
Fluoride, lead have held within a few points between the two most recent periods with enough samples.
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 (9% of 1,368 samples), radium (226 + 228) (8% of 13 samples), and lead (2% of 187 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 (2,445 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 Baltimore County
- 1Nitrate9% of 1,368 local samples were above the limit.
- 2Radium (226 + 228)8% of 13 local samples were above the limit.
- 3Lead2% of 187 local samples were above the limit.
- 4Coliform bacteriaRecommended for every private well, every year.
- 5RadonMedian local reading is 2,445 pCi/L.
- 6ChlorideDetected in 100% of local samples.
- 7CopperDetected in 89% of local samples.
- 8Volatile organic compounds (VOCs)4 hazardous waste sites on record locally.
- 9Metals panel4 hazardous waste sites on record locally.
Test your Baltimore County well for nitrate, radium (226 + 228) and lead
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 Baltimore County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
The rock under Baltimore 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 Baltimore County
MDE Land Restoration Program sites records 4 hazardous waste sites in Baltimore County, among 239 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.
- 4
- hazardous waste sitesSolvents, degreasers and metals from industrial sites can travel far in fractured bedrock.
- 235
- other remediation projects
Treatment that fits the local profile
Nitrate
Point-of-use reverse osmosis; Anion exchange; Distillation
Radium (226 + 228)
Water softener (cation exchange); Point-of-use reverse osmosis
Lead
Point-of-use reverse osmosis; Certified lead-removal carbon filter; Neutralizing filter to raise pH and stop leaching
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 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.
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Common questions
Is there arsenic in well water in Baltimore County?
Arsenic was detected in 9% of 138 public well samples in Baltimore County, and 0% 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 Baltimore County?
The median radon level across 180 public samples in Baltimore County was 2,445 pCi/L, with a high of 28,600 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Baltimore 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 Baltimore 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: 4,949 samples in Baltimore 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 131,371 people on private wells in Baltimore 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: 239 regulated sites located in Baltimore 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.