Private Well Water Testing in Maryland
County-by-county USGS area-risk estimates for private wells across Maryland — arsenic exceedance probability and private-well population — plus how to test your own well at a Maryland-certified laboratory.
Maryland private-well risk summary
Counties covered
24
Maryland counties with modeled risk data.
People on private wells
area estimate732,360
estimated across covered Maryland counties.
Average arsenic risk
area estimate4%
average modeled chance a well exceeds 10 µg/L arsenic across covered counties.
Maryland counties
- Anne Arundel County4% arsenic exceedance (area estimate)88,042 people on private wells
- Frederick County3% arsenic exceedance (area estimate)59,532 people on private wells
- Carroll County3% arsenic exceedance (area estimate)58,743 people on private wells
- Baltimore County3% arsenic exceedance (area estimate)58,022 people on private wells
- Harford County3% arsenic exceedance (area estimate)55,167 people on private wells
- St. Mary's County6% arsenic exceedance (area estimate)40,588 people on private wells
- Cecil County3% arsenic exceedance (area estimate)36,454 people on private wells
- Charles County4% arsenic exceedance (area estimate)34,424 people on private wells
- Wicomico County2% arsenic exceedance (area estimate)34,406 people on private wells
- Montgomery County4% arsenic exceedance (area estimate)32,154 people on private wells
- Washington County3% arsenic exceedance (area estimate)26,540 people on private wells
- Queen Anne's County4% arsenic exceedance (area estimate)26,474 people on private wells
- Calvert County4% arsenic exceedance (area estimate)26,417 people on private wells
- Howard County4% arsenic exceedance (area estimate)24,066 people on private wells
- Caroline County3% arsenic exceedance (area estimate)20,911 people on private wells
- Garrett County4% arsenic exceedance (area estimate)16,658 people on private wells
- Talbot County5% arsenic exceedance (area estimate)15,395 people on private wells
- Worcester County4% arsenic exceedance (area estimate)15,394 people on private wells
- Somerset County5% arsenic exceedance (area estimate)13,810 people on private wells
- Prince George's County2% arsenic exceedance (area estimate)13,354 people on private wells
- Dorchester County5% arsenic exceedance (area estimate)13,122 people on private wells
- Allegany County3% arsenic exceedance (area estimate)12,871 people on private wells
- Kent County4% arsenic exceedance (area estimate)9,171 people on private wells
- Baltimore city3% arsenic exceedance (area estimate)645 people on private wells
Find a Maryland-certified testing lab
Get your well tested at a Maryland-certified laboratory. We list certification programs by state.
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Upload my well testThese figures are USGS area estimates: statistical groundwater models describing how likely elevated contaminant levels are across a county. They are not designed to predict the concentration in any single well. Only testing your own well reveals its water quality.
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