Health problems are rare in tested Calvert County wells.

All 5 health checks came back rare here.

From 10 wells tested in Calvert County since 2001; your own well needs its own test. How to read this

Tested wells over the limit CalvertMaryland

Manganese0%0 of 10 Radon0%0 of 10 Nitrate0%0 of 10 Arsenic0%0 of 10 Fluoride0%0 of 10

StainsNot a health risk

Iron stains40%4 of 10

Not charted, because fewer than 10 wells were tested: uranium (8), lead (8).

Rare: under 5%Worth checking: 5 to 15%Widespread: 15%+

Lab results: Water Quality Portal (USGS and EPA)

Show iron

Who drinks from a well here

7 in 10 people 62,337 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)

LowMiddleHigh

Likely here. Test your home's air first.

Radon zones: EPA map

Here's how Calvert County compares with Maryland and the counties around it.

Each result puts Calvert County next to the 6 counties that border it, on the chart's 0 to 50% scale.

All 5 health checks are rare in Calvert County.

Manganese0 of 10 wells over

None of the 10 wells tested here from 2001 to 2016 were over the EPA health advisory of 0.3 mg/L, against about 2 in 10 across Maryland. Half the results were under 0.0074 mg/L, and the top 1 in 10 were 0.083 mg/L or more. Calvert County had none, while 12 of the 17 other Maryland counties with 10 or more tested wells had at least one.

Calvert and its neighbors

Dorchester27%

Anne Arundel9%

Charles5%

Calvert0%

St. Mary's0%

Talbot0%

Too few tested to show: Prince George's.

Manganese guide

Radon in water0 of 10 wells over

None of the 10 wells tested here from 2001 to 2016 were over 4,000 pCi/L, a level the EPA proposed, against about 1 in 10 across Maryland. Half the results were under 222 pCi/L, and the top 1 in 10 were 430 pCi/L or more. Calvert County had none, while 3 of the 10 other Maryland counties with 10 or more tested wells had at least one.

Calvert and its neighbors

Anne Arundel0%

Calvert0%

Charles0%

Dorchester0%

Talbot0%

Too few tested to show: Prince George's, St. Mary's.

Radon guide

Nitrate0 of 10 wells over

None of the 10 wells tested here from 2001 to 2016 were over the EPA limit of 10 mg/L, against about 1 in 10 across Maryland. Calvert County had none, while 11 of the 17 other Maryland counties with 10 or more tested wells had at least one, leaving out 1 county whose results are likely overstated.

Calvert and its neighbors

Talbot17%

Dorchester7%

Anne Arundel1%

Calvert0%

Charles0%

St. Mary's0%

Too few tested to show: Prince George's.

Nitrate guide

Arsenic0 of 10 wells over

None of the 10 wells tested here from 2001 to 2016 were over the EPA limit of 10 µg/L, against about 1 in 12 across Maryland. Half the results were under 1.6 µg/L, and the top 1 in 10 were 4.9 µg/L or more. Calvert County had none, while 9 of the 15 other Maryland counties with 10 or more tested wells had at least one.

Calvert and its neighbors

Dorchester37%

Talbot23%

St. Mary's12%

Anne Arundel6%

Calvert0%

Charles0%

Too few tested to show: Prince George's.

Arsenic guide

Fluoride0 of 10 wells over

None of the 10 wells tested here from 2001 to 2016 were over the EPA limit of 4 mg/L, against under 1 in 100 across Maryland. Half the results were under 0.29 mg/L, and the top 1 in 10 were 0.39 mg/L or more. Calvert County had none, while 1 of the 17 other Maryland counties with 10 or more tested wells had at least one.

Calvert and its neighbors

Dorchester3%

Anne Arundel0%

Calvert0%

Charles0%

St. Mary's0%

Talbot0%

Too few tested to show: Prince George's.

Too few Calvert County wells were tested for these 2.

Uranium8 wells tested

Only 8 wells here were tested from 2011 to 2016, too few to say how common it is. Across Maryland it's none.

Uranium guide

Lead8 wells tested

Only 8 wells here were tested from 2011 to 2016, too few to say how common it is. Across Maryland it's under 1 in 100.

Lead guide

Every well needs a bacteria test every year.

No bacteria tests from Calvert County wells are in the public data. Test every year anyway.

Iron reached staining levels in 4 of 10 tested wells, and it isn't a health risk.

Iron stains4 of 10 wells had it

About 4 in 10 wells tested here from 2001 to 2016 had enough iron to stain (0.3 mg/L), against about 4 in 10 across Maryland.

Calvert and its neighbors

Anne Arundel72%

Charles63%

Dorchester49%

Calvert40%

Talbot25%

St. Mary's12%

Too few tested to show: Prince George's.

Iron guide

Calvert County has 10 tested wells, and the busiest decade for testing was the 2010s.

2 wells had a test in the 2000s and 8 in the 2010s.

None of the 10 wells has a test from 2020 or later, so a fresh test of your own well tells you more than any of these.

Most Calvert 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 3 things to check in Calvert County.

Bacteria
Nitrate
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 320 feet.

That comes from 20,492 household wells in Maryland's drilling records. Most wells of every kind here are 280 to 380 feet deep. Wells as deep as Calvert 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 go deeper than in 18 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 Calvert County.

Calvert 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 4 town water systems in Calvert County test for PFAS. None found any. No well in Calvert 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

Next door to Calvert County

Anne Arundel St. Mary's Charles

Elsewhere in Maryland

Baltimore Carroll Harford Frederick Montgomery

All of Maryland

Questions people ask about well water in Calvert County

Is well water in Calvert County safe to drink?

Most tested wells in Calvert County came in under the limits. Of 5 health checks with enough tests, nitrate came closest, at 0 of 10 wells over. Every well is different, so test yours for bacteria, nitrate and arsenic.

Where can I get my well tested in Calvert 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 and arsenic, the tests that matter most in Calvert County.

How deep are wells in Calvert County?

Half the household wells here are shallower than 320 feet. Typical household wells here go deeper than in 18 of the 23 other Maryland counties with enough drilling records.

How does Calvert County compare with the counties around it?

For manganese, the share of tested wells over the limit: 3 of the 5 neighboring counties with data had a higher share than Calvert County, at 0%. Dorchester had the most, at 27%. Groundwater doesn't stop at county lines, so Dorchester's 27% is worth knowing about if you live near it.

How often should I test my well in Calvert County?

Calvert County has no public bacteria results for wells, so follow the CDC's advice: test for bacteria and nitrate every year, and right away after a flood, a repair, or any change in taste or smell.

By the Tested Water teamData from the USGS, EPA and Maryland Department of the EnvironmentUpdated November 8, 2026

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Where the Calvert County numbers come from

People on wells: 62,337 in Calvert County, from EPA estimates built on the 2020 Census (Murray et al.).
Lab tests: 81 well water samples from 10 wells in the Water Quality Portal, run by the USGS and EPA, 2001 to 2016.
Well depths: 20,492 Maryland drilling records for Calvert County, gathered in the US Groundwater Well Database (Lin and others, 2024).
Neighboring counties: the 6 counties that share a border with Calvert County, from the Census Bureau's county adjacency file.
PFAS: EPA tests of 4 town water systems in Calvert County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
Radon: Calvert County is zone 1 on the EPA Map of Radon Zones.
State programs and links: Maryland Department of the Environment, checked November 1, 2026.

Download this county's data (CSV)How we read these numbers Report an error