Health problems are rare in tested Jefferson County wells.

All 7 health checks came back rare here.

From 25 wells tested in Jefferson County since 2005; your own well needs its own test. How to read this

Tested wells over the limit JeffersonNew York

Manganese0%0 of 25 Arsenic0%0 of 25 Nitrate0%0 of 25 Lead0%0 of 25 Radon0%0 of 19 Uranium0%0 of 25 Fluoride0%0 of 25

GermsTest every year, whatever the chart says

Coliform bacteria21%4 of 19 E. coli12%2 of 16

StainsNot a health risk

Iron stains20%5 of 25

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

Lab results: Water Quality Portal (USGS and EPA)

Show bacteria and iron

Who drinks from a well here

1 in 3 people 41,356 people

Nobody else tests these wells. Only you do.

People on wells: EPA researchers' 2020 estimate

How deep wells go here

Middle depth: some shelter from the surface, not complete.

Well depths: US Groundwater Well Database

Radon risk (a gas from rock)

LowMiddleHigh

Possible here. A home air test is inexpensive.

Radon zones: EPA map

Here's how Jefferson County compares with New York and the counties around it.

Each result puts Jefferson County next to the 4 counties that border it, on the chart's 0 to 50% scale.

All 7 health checks are rare in Jefferson County.

Manganese0 of 25 wells over

None of the 25 wells tested here from 2005 to 2020 were over the EPA health advisory of 0.3 mg/L, against about 1 in 7 across New York. Half the results were under 0.0086 mg/L, and the top 1 in 10 were 0.067 mg/L or more. Jefferson County had none, while 37 of the 50 other New York counties with 10 or more tested wells had at least one, leaving out 1 county whose results are likely overstated.

Jefferson and its neighbors

Oswego9%

St. Lawrence5%

Lewis5%

Cayuga0%

Jefferson0%

Manganese guide

Arsenic0 of 25 wells over

None of the 25 wells tested here from 2005 to 2020 were over the EPA limit of 10 µg/L, against about 1 in 28 across New York. At least half the results were too low for the lab to measure, and the top 1 in 10 were 1.0 µg/L or more. Jefferson County had none, while 23 of the 49 other New York counties with 10 or more tested wells had at least one.

Jefferson and its neighbors

Oswego5%

Cayuga0%

Jefferson0%

Lewis0%

St. Lawrence0%

Arsenic guide

Nitrate0 of 25 wells over

None of the 25 wells tested here from 2005 to 2020 were over the EPA limit of 10 mg/L, against about 1 in 35 across New York. Half the results were under 0.09 mg/L, and the top 1 in 10 were 0.98 mg/L or more. Jefferson County had none, while 9 of the 51 other New York counties with 10 or more tested wells had at least one.

Jefferson and its neighbors

St. Lawrence2%

Cayuga0%

Jefferson0%

Lewis0%

Oswego0%

Nitrate guide

Lead0 of 25 wells over

None of the 25 wells tested here from 2005 to 2020 were over the EPA action level of 15 µg/L, against about 1 in 40 across New York. Half the results were under 0.15 µg/L, and the top 1 in 10 were 1.3 µg/L or more. Jefferson County had none, while 3 of the 51 other New York counties with 10 or more tested wells had at least one.

Jefferson and its neighbors

Cayuga0%

Jefferson0%

Lewis0%

Oswego0%

St. Lawrence0%

Lead guide

Radon in water0 of 19 wells over

None of the 19 wells tested here from 2005 to 2020 were over 4,000 pCi/L, a level the EPA proposed, against under 1 in 50 across New York. Half the results were under 269 pCi/L, and the top 1 in 10 were 1,020 pCi/L or more. Jefferson County had none, while 7 of the 45 other New York counties with 10 or more tested wells had at least one.

Jefferson and its neighbors

St. Lawrence7%

Cayuga0%

Jefferson0%

Lewis0%

Oswego0%

Radon guide

Uranium0 of 25 wells over

None of the 25 wells tested here from 2005 to 2020 were over the EPA limit of 30 µg/L, against under 1 in 100 across New York. Half the results were under 0.33 µg/L, and the top 1 in 10 were 1.4 µg/L or more. Jefferson County had none, while 3 of the 46 other New York counties with 10 or more tested wells had at least one.

Jefferson and its neighbors

St. Lawrence2%

Cayuga0%

Jefferson0%

Lewis0%

Oswego0%

Uranium guide

Fluoride0 of 25 wells over

None of the 25 wells tested here from 2005 to 2020 were over the EPA limit of 4 mg/L, against under 1 in 100 across New York. Half the results were under 0.29 mg/L, and the top 1 in 10 were 1.1 mg/L or more. Jefferson County had none, while 2 of the 51 other New York counties with 10 or more tested wells had at least one.

Jefferson and its neighbors

Cayuga8%

Jefferson0%

Lewis0%

Oswego0%

St. Lawrence0%

Coliform bacteria turned up in 4 of 19 tested Jefferson County wells, so test for it every year.

Coliform bacteria4 of 19 wells had it

About 2 in 10 wells tested here from 2005 to 2020 had coliform bacteria, against about 1 in 4 across New York.

Jefferson and its neighbors

Cayuga33%

Jefferson21%

Oswego20%

St. Lawrence20%

Lewis14%

Bacteria guide

E. coli2 of 16 wells had it

2 of 16 wells tested here from 2005 to 2020 had E. coli, against about 1 in 26 across New York.

Jefferson and its neighbors

Jefferson12%

St. Lawrence12%

Cayuga0%

Lewis0%

Oswego0%

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 5 of 25 tested wells, and it isn't a health risk.

Iron stains5 of 25 wells had it

About 2 in 10 wells tested here from 2005 to 2020 had enough iron to stain (0.3 mg/L), against about 4 in 10 across New York.

Jefferson and its neighbors

Cayuga38%

St. Lawrence28%

Lewis27%

Oswego27%

Jefferson20%

Iron guide

Jefferson County has 25 tested wells, and the busiest decade for testing was the 2010s.

9 wells had a test in the 2000s, 18 in the 2010s and 1 since 2020.

Only 1 of the 25 wells have a test from 2020 or later, so a fresh test of your own well tells you more than any of these.

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 New York offers well owners

Free testingThe Private Well PFAS Testing and Mitigation Rebate Pilot Program offers limited free PFAS testing and treatment rebates in Dutchess, Orange, Putnam, Suffolk, Ulster and Westchester counties. See the program
Certified labsNew York's list of certified labs
Well recordsNew York's well record search

Half the household wells here are shallower than 103 feet.

That comes from 2,466 household wells in New York's drilling records. Most wells of every kind here are 70 to 158 feet deep. Wells as deep as Jefferson 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 41 of the 56 other New York counties with enough drilling records.

Look up your own well's depth in New York's well record search, or see how to find it.

Well depths: US Groundwater Well Database

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

Jefferson County is in the EPA's middle radon zone. An indoor air test is cheap and tells you whether to look at your water. Radon guide

Between 2023 and 2025 the EPA had 4 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 7.3 ng/L of PFOA. No well in Jefferson 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 Jefferson County

St. Lawrence Oswego

Elsewhere in New York

Orange Ulster Saratoga Oneida Rensselaer Steuben

All of New York

Questions people ask about well water in Jefferson County

Is well water in Jefferson County safe to drink?

Most tested wells in Jefferson County came in under the limits. Of 7 health checks with enough tests, nitrate came closest, at 0 of 25 wells over. Every well is different, so test yours for bacteria, nitrate and arsenic.

Can I get my well tested for free in Jefferson County?

The Private Well PFAS Testing and Mitigation Rebate Pilot Program offers limited free PFAS testing and treatment rebates in Dutchess, Orange, Putnam, Suffolk, Ulster and Westchester counties. If not, use a lab New York has certified for drinking water. Ask for bacteria, nitrate and arsenic, the tests that matter most in Jefferson County.

How deep are wells in Jefferson County?

Half the household wells here are shallower than 103 feet. Typical household wells here are shallower than in 41 of the 56 other New York counties with enough drilling records.

How does Jefferson County compare with the counties around it?

For manganese, the share of tested wells over the limit: 3 of the 4 neighboring counties with data had a higher share than Jefferson County, at 0%. Oswego had the most, at 9%. Groundwater doesn't stop at county lines, so Oswego's 9% is worth knowing about if you live near it.

How often should I test my well in Jefferson County?

In Jefferson County, 4 of 19 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 HealthUpdated November 8, 2026

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Where the Jefferson County numbers come from

People on wells: 41,356 in Jefferson County, from EPA estimates built on the 2020 Census (Murray et al.).
Lab tests: 271 well water samples from 25 wells in the Water Quality Portal, run by the USGS and EPA, 2005 to 2020.
Well depths: 2,466 New York drilling records for Jefferson County, gathered in the US Groundwater Well Database (Lin and others, 2024).
Neighboring counties: the 4 counties that share a border with Jefferson County, from the Census Bureau's county adjacency file.
PFAS: EPA tests of 4 town water systems in Jefferson County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
Radon: Jefferson County is zone 2 on the EPA Map of Radon Zones.
State programs and links: Department of Health, checked November 1, 2026.

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