Manganese is widespread in Montgomery County wells.
1 widespread, 5 rare out of 6 health checks.
From 31 wells tested in Montgomery County since 2001; your own well needs its own test. How to read this
Not charted, because fewer than 10 wells were tested: radon (8).
Rare: under 5%Worth checking: 5 to 15%Widespread: 15%+
Lab results: Water Quality Portal (USGS and EPA)
Who drinks from a well here
About 1 in 16 people 65,389 people
Nobody else tests these wells. Only you do.
People on wells: EPA researchers' 2020 estimate
How deep wells go here
Deep wells: fewer surface germs, more minerals from the rock.
Well depths: US Groundwater Well Database
Radon risk (a gas from rock)
Likely here. Test your home's air first.
Radon zones: EPA map
Here's how Montgomery County compares with Maryland and the counties around it.
Each result puts Montgomery County next to the 7 counties that border it, on the chart's 0 to 50% scale.
This one is widespread in Montgomery County wells.
Manganese6 of 30 wells over
Too few tested to show: Arlington, VA, Howard, Loudoun, VA, Prince George's.
These 5 are rare in Montgomery County.
Nitrate1 of 30 wells over
Too few tested to show: Arlington, VA, Howard, Loudoun, VA, Prince George's.
Arsenic0 of 22 wells over
Too few tested to show: Arlington, VA, Howard, Loudoun, VA, Prince George's.
Lead0 of 22 wells over
Too few tested to show: Arlington, VA, Howard, Loudoun, VA, Prince George's.
Fluoride0 of 30 wells over
Too few tested to show: Arlington, VA, Howard, Loudoun, VA, Prince George's.
Uranium0 of 19 wells over
Too few tested to show: Arlington, VA, Frederick, Howard, Loudoun, VA, Prince George's.
Too few Montgomery County wells were tested for this one.
Radon in water8 wells tested
Coliform bacteria turned up in 3 of 5 tested Montgomery County wells, so test for it every year.
Coliform bacteria3 of 5 wells had it
E. coli1 of 5 wells had it
E. coli means human or animal waste is getting in, so if a test of your Montgomery County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 11 of 30 tested wells, and it isn't a health risk.
Iron stains11 of 30 wells had it
Too few tested to show: Arlington, VA, Howard, Loudoun, VA, Prince George's.
Montgomery County has 31 tested wells, and the busiest decade for testing was the 2000s.
Only 2 of the 31 wells have a test from 2020 or later, so a fresh test of your own well tells you more than any of these.
Most Montgomery County wells in these records were tested for research or because someone suspected a problem, which can push the shares above what a typical home well would show (how we read the numbers).
One mail-in lab test covers the 4 things to check in Montgomery County.
- Bacteria
- Nitrate
- Manganese
- Arsenic
What Maryland offers well owners
- Free testingWe didn't find a free program for all of Maryland. Maryland's private well page
- Certified labsMaryland's list of certified labs
- Well recordsWe didn't find an online search.
- New wellsSince October 1, 2024, Md. Code, Real Property 10-713 requires a contract for sale of property with a private well to make well water quality testing a condition of sale, with both parties certifying they reviewed the results.
Half the household wells here are shallower than 150 feet.
That comes from 15,407 household wells in Maryland's drilling records. Most wells of every kind here are 105 to 300 feet deep. Wells as deep as Montgomery County's are usually better protected from fertilizer and bacteria at the surface, but they can pick up more of what's in the rock, like arsenic and uranium. Typical household wells here are shallower than in 15 of the 23 other Maryland counties with enough drilling records.
How to find your own well's depth
Well depths: US Groundwater Well Database
Here's what we know about radon and PFAS in Montgomery County.
Montgomery County is in the EPA's highest radon zone. Radon from well water adds to the radon in your indoor air, so test your air first, and your water too if the air is high. Radon guide
Between 2023 and 2025 the EPA had 3 town water systems in Montgomery County test for PFAS. 1 of them had at least one test above 4 ng/L, the new EPA limit for PFOA and PFOS. The highest single result was 6.5 ng/L of PFOS. No well in Montgomery County has public PFAS results, so the town systems are the best clue to what's in the groundwater nearby. PFAS guide
Radon zones: EPA Map of Radon Zones. PFAS: EPA tests of town water systems, 2023 to 2025
Questions people ask about well water in Montgomery County
Is well water in Montgomery County safe to drink?
6 of 30 wells tested in Montgomery County had manganese over the limit, about 2 in 10. Across Maryland it's about 2 in 10. That's a bigger share than in 14 of the 17 other Maryland counties with 10 or more tested wells. So test your own well for manganese before you count on it.
Where can I get my well tested in Montgomery County?
Use a lab Maryland has certified for drinking water. Maryland's list is linked above, in the box about testing. Ask for bacteria, nitrate, manganese and arsenic, the tests that matter most in Montgomery County.
How deep are wells in Montgomery County?
Half the household wells here are shallower than 150 feet. Typical household wells here are shallower than in 15 of the 23 other Maryland counties with enough drilling records.
How does Montgomery County compare with the counties around it?
For manganese, the share of tested wells over the limit: 1 of the 3 neighboring counties with data had a higher share than Montgomery County, at 20%. District of Columbia, DC had the most, at 50%. Groundwater doesn't stop at county lines, so District of Columbia, DC's 50% is worth knowing about if you live near it.
How often should I test my well in Montgomery County?
In Montgomery County, 3 of 5 tested wells had coliform bacteria, so the CDC's advice matters here: test for bacteria and nitrate every year, and right away after a flood, a repair, or any change in taste or smell.
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Where the Montgomery County numbers come from
- People on wells: 65,389 in Montgomery County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 368 well water samples from 31 wells in the Water Quality Portal, run by the USGS and EPA, 2001 to 2020.
- Well depths: 15,407 Maryland drilling records for Montgomery County, gathered in the US Groundwater Well Database (Lin and others, 2024).
- Neighboring counties: the 7 counties that share a border with Montgomery County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 3 town water systems in Montgomery County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Montgomery County is zone 1 on the EPA Map of Radon Zones.
- State programs and links: Maryland Department of the Environment, checked November 1, 2026.