Well water in Maryland
1in6
Testing recommended
tested well samples in Maryland exceeded the EPA limit for nitrate (10 mg/L), based on public data from USGS Water Quality Portal.
45,600 test results across 15 contaminants from at least 3,617 wells, 1919 to 2025; nitrate has the most at 10,124. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
An estimated 1,423,948 people in Maryland get their drinking water from a private well, per USGS 2015 county water use.
Separately, the USGS national arsenic model estimates that 3% of the 1,423,948 people on private wells in Maryland draw water above 10 ug/L (the model's range is 2% to 4%), from geology and well depth rather than local tests.
What individual samples found
Each row summarizes every public sample for that contaminant inside Maryland. 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 1919 to 2025 | 10,124 | 80% | 2.08 | 9,740 | 10 mg/L EPA limit | |
| Radium (226 + 228) 1955 to 2019 | 442 | 65% | 0.325 | 44 | 5 pCi/L EPA limit | |
| E. coli 1994 to 2024 | 76 | 8% | 0 | 200 | 0 MPN/100mL EPA limit | |
| Arsenic 1957 to 2025 | 1,462 | 47% | 0 | 111 | 10 ug/L EPA limit | |
| Lead 1957 to 2025 | 1,730 | 44% | 0 | 500 | 15 ug/L EPA limit | |
| Copper 1944 to 2025 | 2,024 | 51% | 0 | 4.2 | 1.3 mg/L EPA limit | |
| Fluoride 1938 to 2025 | 4,657 | 65% | 0.1 | 180 | 4 mg/L EPA limit | |
| Uranium 1955 to 2025 | 764 | 49% | 0 | 18.4 | 30 ug/L EPA limit | |
| Chloride 1919 to 2025 | no limit | 7,776 | 100% | 12.6 | 42,600 | 250 mg/L nuisance level |
| Iron 1919 to 2025 | no limit | 5,693 | 87% | 130 | 656,000 | 300 ug/L nuisance level |
| Sodium 1932 to 2025 | no limit | 5,193 | 100% | 10 | 22,400 | 20 mg/L health guideline |
| Manganese 1945 to 2025 | no limit | 4,799 | 83% | 20 | 222,000 | 300 ug/L health guideline |
| Radon 1988 to 2020 | no limit | 852 | 96% | 450 | 42,000 | 2,000 pCi/L health guideline |
Sampled fewer than 10 times, too few to summarize: PFOS (4), PFOA (4).
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 | 17%7,488 samples | 17%1,857 samples | 26%673 samples | 20%106 samples |
| Fluoride | <1%3,484 samples | 0%738 samples | <1%382 samples | 0%53 samples |
| Copper | <1%1,361 samples | 0%133 samples | 0%430 samples | 0%100 samples |
| Lead | 3%947 samples | 1%253 samples | 0%430 samples | 1%100 samples |
| Arsenic | 2%707 samples | 5%270 samples | 5%385 samples | 1%100 samples |
| Uranium | 0%107 samples | 0%126 samples | 0%431 samples | 0%100 samples |
Nitrate above the limit in Maryland fell from 26% of 673 samples in the 2010s to 20% of 106 in the 2020s.
Fluoride, copper, lead, arsenic, uranium have held within a few points between the two most recent periods with enough samples.
What this means
The contaminants most often above their limit here are nitrate (18% of 10,124 samples), radium (226 + 228) (10% of 442 samples), and e. coli (8% of 76 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.
What to test for in Maryland
- 1Nitrate18% of 10,124 local samples were above the limit.
- 2Radium (226 + 228)10% of 442 local samples were above the limit.
- 3E. coli8% of 76 local samples were above the limit.
- 4Arsenic3% of 1,462 local samples were above the limit.
- 5Lead2% of 1,730 local samples were above the limit.
- 6Copper<1% of 2,024 local samples were above the limit.
- 7Fluoride<1% of 4,657 local samples were above the limit.
- 8Volatile organic compounds (VOCs)27 hazardous waste sites on record locally.
- 9Metals panel27 hazardous waste sites on record locally.
Test your Maryland well for nitrate, radium (226 + 228) and E. coli
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 Maryland numbers, $29. Every line explained, ranked by what matters, with the fix for each.
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Send me the Maryland report
The numbers above, which tests to order and where, and the treatment that fits the local profile, in one email.
The rock under Maryland
Northern Atlantic Coastal Plain aquifer system
Semiconsolidated sand. Coastal plain sands like these give steady yields at moderate depth. Salt water and sodium are the usual issues near the coast, and nitrate where the water table is shallow; arsenic and radon from bedrock are less common.
Classification from the USGS Principal Aquifers of the United States (national map, 2003 edition, GIS release 2015), read at the state 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 Maryland
MDE Land Restoration Program sites records 27 hazardous waste sites in Maryland, among 2,077 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.
- 27
- hazardous waste sitesSolvents, degreasers and metals from industrial sites can travel far in fractured bedrock.
- 2,050
- 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
E. coli
Shock chlorination and fix the well cap or casing; UV disinfection whole-house; Chlorination system
Arsenic
Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
Lead
Point-of-use reverse osmosis; Certified lead-removal carbon filter; Neutralizing filter to raise pH and stop leaching
Systems we would look at first
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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 E. coli
UV disinfection system
whole-house, at the point of entry, about $900
Fix the well cap and casing first; UV keeps bacteria from returning.
For E. coli
Aquasana Rhino Well Water with UV
whole-house, at the point of entry, about $2,871
Whole-house system built for wells: sediment pre-filter, KDF and carbon, and a UV lamp rated to kill 99.99% of bacteria and viruses. It does not remove arsenic, nitrate, uranium or radon.
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 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.
Common questions
Is there arsenic in well water in Maryland?
Arsenic was detected in 47% of 1,462 public well samples in Maryland, and 3% 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 Maryland?
The median radon level across 852 public samples in Maryland was 450 pCi/L, with a high of 42,000 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Maryland?
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 in Maryland
- Allegany3% nitrate
- Anne Arundel23% radium (226 + 228)
- Baltimore9% nitrate
- Baltimore9% nitrate
- Calvert31% nitrate
- Caroline28% nitrate
- Carroll20% nitrate
- Cecil7% nitrate
- Charles1% nitrate
- Dorchester24% arsenic
- Frederick17% nitrate
- Garrett4% arsenic
- Harford11% nitrate
- Howard8% lead
- Kent50% nitrate
- Montgomery13% nitrate
- Prince George's3% nitrate
- Queen Anne's40% nitrate
- Somerset6% lead
- St. Mary's10% arsenic
- Talbot8% nitrate
- Washington37% nitrate
- Wicomico13% nitrate
- Worcester6% nitrate
Want the numbers themselves? Download the Maryland dataset as CSV, every county and town, with the sources named.
Sources
- USGS Water Quality Portal: 45,600 samples in Maryland. 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 1,423,948 people on private wells in Maryland 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: 2,077 regulated sites located in Maryland. 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.