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.
These 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.
By TapWaterData Editorial
Stay Informed About Your Water Quality
Get EPA reports, filter recommendations, and safety alerts for your area.
Join 10,000+ people protecting their families. Unsubscribe anytime.