Nitrate, manganese and arsenic have turned up often in Dane County wells, mostly in study samples.
3 likely overstated, 1 worth checking out of 4 health checks.
From 138 wells tested in Dane County since 2000; your own well needs its own test. How to read this
*Nitrate: That's more than 5 times what a 2016 random sample of private wells found across Wisconsin (about 1 in 12), so this likely overstates it.
*Manganese, arsenic and lead: All of these tests come from the US Geological Survey in one small part of the county, so they may not match the rest of the county.
Not charted, because fewer than 10 wells were tested: uranium (1), fluoride (1).
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 8 people 71,806 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 Dane County compares with Wisconsin and the counties around it.
Each result puts Dane County next to the 7 counties that border it, on the chart's 0 to 50% scale.
These 3 have turned up often here, mostly in study samples.
Nitrate59 of 138 wells over
* Likely overstated, so we don't rank it.
That's more than 5 times what a 2016 random sample of private wells found across Wisconsin (about 1 in 12), so this likely overstates it.
Manganese6 of 19 wells over
All of these tests come from the US Geological Survey in one small part of the county, so it may not match the rest of the county.
Arsenic4 of 19 wells over
All of these tests come from the US Geological Survey in one small part of the county, so it may not match the rest of the county.
This one is worth checking in Dane County.
Lead2 of 19 wells over
All of these tests come from the US Geological Survey in one small part of the county, so it may not match the rest of the county.
Too few Dane County wells were tested for these 2.
Uranium1 well tested
Fluoride1 well tested
None of the 1 Dane County wells tested for bacteria had it, but every well needs a yearly test.
Coliform bacteria0 of 1 wells had it
E. coli0 of 1 wells had it
E. coli means human or animal waste is getting in, so if a test of your Dane County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 0 of 19 tested wells, and it isn't a health risk.
Iron stains0 of 19 wells had it
About 5 in 10 of the 138 wells tested in Dane County have a test from 2020 or later.
With 63 wells tested since 2020, age matters less here than who did the testing and why.
Most Dane 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 5 things to check in Dane County.
- Bacteria
- Nitrate
- Manganese
- Arsenic
- Lead
What Wisconsin offers well owners
- Free testingWe didn't find a free program for all of Wisconsin. Wisconsin's private well page
- Certified labsWisconsin's list of certified labs
- Well recordsWisconsin's well record search
- New wellsUnder NR 812.46, the well driller must collect a water sample from any new or reconstructed potable well within 30 days of completion and have it tested for coliform bacteria by a certified lab.
Half the wells on record here are shallower than 180 feet.
That comes from 13,477 wells in Wisconsin's drilling records. Most wells of every kind here are 140 to 243 feet deep. Wells as deep as Dane 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 wells on record here go deeper than in 59 of the 71 other Wisconsin counties with enough drilling records.
Look up your own well's depth in Wisconsin'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 Dane County.
Dane 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 15 town water systems in Dane County test for PFAS. 6 found some PFAS, all below the new limits. No well in Dane 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 Dane County
Is well water in Dane County safe to drink?
59 of 138 wells tested in Dane County had nitrate over the limit, about 4 in 10. Across Wisconsin it's about 1 in 12. We don't rank this against other Wisconsin counties, because most of these tests come from studies. That's more than 5 times what a 2016 random sample of private wells found across Wisconsin (about 1 in 12), so this likely overstates it. So test your own well for nitrate before you count on it.
Where can I get my well tested in Dane County?
Use a lab Wisconsin has certified for drinking water. Wisconsin's list is linked above, in the box about testing. Ask for bacteria, nitrate, manganese, arsenic and lead, the tests that matter most in Dane County.
How deep are wells in Dane County?
Half the wells on record here are shallower than 180 feet. Typical wells on record here go deeper than in 59 of the 71 other Wisconsin counties with enough drilling records.
How does Dane County compare with the counties around it?
For nitrate, the share of tested wells over the limit: 3 of the 7 neighboring counties with data had a higher share than Dane County, at 43%. Iowa had the most, at 65%. Groundwater doesn't stop at county lines, so Iowa's 65% is worth knowing about if you live near it.
How often should I test my well in Dane County?
None of the 1 wells tested for bacteria in Dane County had it, but the CDC still says to 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 Dane County numbers come from
- People on wells: 71,806 in Dane County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 391 well water samples from 138 wells in the Water Quality Portal, run by the USGS and EPA, 2000 to 2025.
- Well depths: 13,477 Wisconsin drilling records for Dane County, gathered in the US Groundwater Well Database (Lin and others, 2024).
- Neighboring counties: the 7 counties that share a border with Dane County, from the Census Bureau's county adjacency file.
- Nitrate for comparison: Wisconsin DATCP, Agricultural Chemicals in Wisconsin Groundwater (2017).
- Results marked likely overstated: our own check of who tested the wells, when and where.
- PFAS: EPA tests of 15 town water systems in Dane County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Dane County is zone 1 on the EPA Map of Radon Zones.
- State programs and links: Department of Natural Resources (DNR), checked November 1, 2026.