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Nitrate is worth checking in Jefferson County wells.

1 worth checking, 6 rare out of 7 health checks.

From 38 wells tested in Jefferson County since 2002; your own well needs its own test. How to read this

Tested wells over the limit JeffersonWest Virginia
Nitrate8%3 of 38Manganese3%1 of 38Arsenic0%0 of 35Lead0%0 of 35Fluoride0%0 of 38Uranium0%0 of 25Radon0%0 of 21
GermsTest every year, whatever the chart says
Coliform bacteria65%13 of 20E. coli20%4 of 20
StainsNot a health risk
Iron stains5%2 of 38

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

Lab results: Water Quality Portal (USGS and EPA)

Who drinks from a well here

1 in 2 people 23,753 people

Nobody else tests these wells. Only you do.

People on wells: EPA researchers' 2020 estimate

Radon risk (a gas from rock)

Likely here. Test your home's air first.

Radon zones: EPA map

Here's how Jefferson County compares with West Virginia and the counties around it.

Each result puts Jefferson County next to the 5 counties that border it, on the chart's 0 to 50% scale.

This one is worth checking in Jefferson County.

Nitrate3 of 38 wells over

3 of 38 wells tested here from 2002 to 2022 were over the EPA limit of 10 mg/L, against under 1 in 100 across West Virginia. Half the results were under 3.6 mg/L, and the top 1 in 10 were 8.5 mg/L or more. That's the highest share among the 13 West Virginia counties with 10 or more tested wells.

Jefferson and its neighbors
Washington, MD12%
Jefferson8%
Clarke, VA0%

Too few tested to show: Berkeley, Frederick, VA, Loudoun, VA.

Nitrate guide

These 6 are rare in Jefferson County.

Manganese1 of 38 wells over

1 of 38 wells tested here from 2002 to 2022 was over the EPA health advisory of 0.3 mg/L, against about 1 in 4 across West Virginia. At least half the results were too low for the lab to measure, and the top 1 in 10 were 0.022 mg/L or more. That's the lowest share among the 13 West Virginia counties with 10 or more tested wells.

Jefferson and its neighbors
Jefferson3%
Clarke, VA0%
Washington, MD0%

Too few tested to show: Berkeley, Frederick, VA, Loudoun, VA.

Manganese guide

Arsenic0 of 35 wells over

None of the 35 wells tested here from 2002 to 2022 were over the EPA limit of 10 µg/L, against about 1 in 19 across West Virginia. Jefferson County had none, while 5 of the 12 other West Virginia counties with 10 or more tested wells had at least one.

Jefferson and its neighbors
Jefferson0%
Washington, MD0%

Too few tested to show: Berkeley, Clarke, VA, Frederick, VA, Loudoun, VA.

Arsenic guide

Lead0 of 35 wells over

None of the 35 wells tested here from 2002 to 2022 were over the EPA action level of 15 µg/L, against under 1 in 50 across West Virginia. Jefferson County had none, while 3 of the 12 other West Virginia counties with 10 or more tested wells had at least one.

Jefferson and its neighbors
Clarke, VA0%
Jefferson0%
Washington, MD0%

Too few tested to show: Berkeley, Frederick, VA, Loudoun, VA.

Lead guide

Fluoride0 of 38 wells over

None of the 38 wells tested here from 2002 to 2022 were over the EPA limit of 4 mg/L, against under 1 in 100 across West Virginia. At least half the results were too low for the lab to measure, and the top 1 in 10 were 0.38 mg/L or more. Jefferson County had none, and neither did any of the 12 other West Virginia counties with 10 or more tested wells.

Jefferson and its neighbors
Clarke, VA0%
Jefferson0%
Washington, MD0%

Too few tested to show: Berkeley, Frederick, VA, Loudoun, VA.

Uranium0 of 25 wells over

None of the 25 wells tested here from 2002 to 2022 were over the EPA limit of 30 µg/L, against none across West Virginia. Half the results were under 0.46 µg/L, and the top 1 in 10 were 1.0 µg/L or more.

Uranium guide

Radon in water0 of 21 wells over

None of the 21 wells tested here from 2002 to 2013 were over 4,000 pCi/L, a level the EPA proposed, against none across West Virginia. Half the results were under 650 pCi/L, and the top 1 in 10 were 1,110 pCi/L or more. Jefferson County had none, and neither did any of the 11 other West Virginia counties with 10 or more tested wells.

Radon guide

Coliform bacteria turned up in 13 of 20 tested Jefferson County wells, so test for it every year.

Coliform bacteria13 of 20 wells had it

About 2 in 3 wells tested here from 2002 to 2022 had coliform bacteria, against about 6 in 10 across West Virginia.

Jefferson and its neighbors
Jefferson65%
Berkeley63%

Too few tested to show: Clarke, VA, Frederick, VA, Loudoun, VA, Washington, MD.

Bacteria guide

E. coli4 of 20 wells had it

About 2 in 10 wells tested here from 2002 to 2022 had E. coli, against about 1 in 7 across West Virginia.

Jefferson and its neighbors
Berkeley31%
Jefferson20%

Too few tested to show: Clarke, VA, Frederick, VA, Loudoun, VA, Washington, MD.

E. coli means human or animal waste is getting in, so if a test of your Jefferson County well finds it, boil drinking water until the well is fixed.

Bacteria guide

Iron reached staining levels in 2 of 38 tested wells, and it isn't a health risk.

Iron stains2 of 38 wells had it

2 of 38 wells tested here from 2002 to 2022 had enough iron to stain (0.3 mg/L), against about 5 in 10 across West Virginia.

Jefferson and its neighbors
Washington, MD7%
Jefferson5%
Clarke, VA0%

Too few tested to show: Berkeley, Frederick, VA, Loudoun, VA.

Iron guide

Most of the 38 wells tested in Jefferson County were last tested before 2010.

26 wells had a test in the 2000s, 4 in the 2010s and 12 since 2020.

An old result shows the water as it was then, so treat these 38 wells as a starting point and test your own.

Most Jefferson 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 Jefferson County.

  • Bacteria
  • Nitrate
  • Arsenic

What West Virginia offers well owners

Here's what we know about radon and PFAS in Jefferson County.

Jefferson 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 Jefferson 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 17 ng/L of PFOS. Only 7 wells in Jefferson County have 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 Jefferson County
Washington, MD
Elsewhere in West Virginia
KanawhaBooneHampshirePreston

All of West Virginia

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Questions people ask about well water in Jefferson County

Is well water in Jefferson County safe to drink?

3 of 38 wells tested in Jefferson County had nitrate over the limit, about 1 in 13. Across West Virginia it's under 1 in 100. That's the highest share among the 13 West Virginia counties with 10 or more tested wells. So test your own well for nitrate before you count on it.

Where can I get my well tested in Jefferson County?

Use a lab West Virginia has certified for drinking water. West Virginia's list is linked above, in the box about testing. Ask for bacteria, nitrate and arsenic, the tests that matter most in Jefferson County.

How does Jefferson County compare with the counties around it?

For nitrate, the share of tested wells over the limit: 1 of the 2 neighboring counties with data had a higher share than Jefferson County, at 8%. Washington, MD had the most, at 12%. Groundwater doesn't stop at county lines, so Washington, MD's 12% is worth knowing about if you live near it.

How often should I test my well in Jefferson County?

In Jefferson County, 13 of 20 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.

By the Tested Water teamData from the USGS, EPA and Department of Health, Office of Environmental Health Services, with local health departmentsUpdated November 8, 2026

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Where the Jefferson County numbers come from

  • People on wells: 23,753 in Jefferson County, from EPA estimates built on the 2020 Census (Murray et al.).
  • Lab tests: 337 well water samples from 38 wells in the Water Quality Portal, run by the USGS and EPA, 2002 to 2022.
  • Neighboring counties: the 5 counties that share a border with Jefferson County, from the Census Bureau's county adjacency file.
  • PFAS: EPA tests of 3 town water systems in Jefferson County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
  • Radon: Jefferson County is zone 1 on the EPA Map of Radon Zones.
  • State programs and links: Department of Health, Office of Environmental Health Services, with local health departments, checked November 1, 2026.
Download this county's data (CSV)How we read these numbersReport an error
One lab test covers what to check in Jefferson CountyFind a lab test