Nitrate has turned up often in Portage County wells, mostly in study samples.
1 likely overstated, 5 rare out of 6 health checks.
From 175 wells tested in Portage 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.
Not charted, because fewer than 10 wells were tested: radon (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 2 people 33,322 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)
Likely here. Test your home's air first.
Radon zones: EPA map
Here's how Portage County compares with Wisconsin and the counties around it.
Each result puts Portage County next to the 6 counties that border it, on the chart's 0 to 50% scale.
This one has turned up often here, mostly in study samples.
Nitrate85 of 174 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.
These 5 are rare in Portage County.
Manganese1 of 34 wells over
Too few tested to show: Adams, Marathon, Wood.
Arsenic0 of 32 wells over
Too few tested to show: Adams, Marathon, Wood.
Lead0 of 32 wells over
Too few tested to show: Adams, Marathon, Wood.
Uranium0 of 32 wells over
Too few tested to show: Adams, Marathon, Wood.
Too few Portage County wells were tested for this one.
Radon in water1 well tested
None of the 1 Portage 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 Portage County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 2 of 35 tested wells, and it isn't a health risk.
Iron stains2 of 35 wells had it
Too few tested to show: Adams, Marathon, Wood.
About 4 in 10 of the 175 wells tested in Portage County have a test from 2020 or later.
With 64 wells tested since 2020, age matters less here than who did the testing and why.
Most Portage 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 Portage County.
- Bacteria
- Nitrate
- Arsenic
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 84 feet.
That comes from 7,756 wells in Wisconsin's drilling records. Most wells of every kind here are 50 to 128 feet deep. Wells as deep as Portage 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 are shallower than in 53 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 Portage County.
Portage 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 2 town water systems in Portage County test for PFAS. 1 found some PFAS, all below the new limits. No well in Portage 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 Portage County
Is well water in Portage County safe to drink?
85 of 174 wells tested in Portage County had nitrate over the limit, about 5 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 Portage 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 and arsenic, the tests that matter most in Portage County.
How deep are wells in Portage County?
Half the wells on record here are shallower than 84 feet. Typical wells on record here are shallower than in 53 of the 71 other Wisconsin counties with enough drilling records.
How does Portage County compare with the counties around it?
For nitrate, the share of tested wells over the limit: 2 of the 6 neighboring counties with data had a higher share than Portage County, at 49%. Adams had the most, at 63%. Groundwater doesn't stop at county lines, so Adams's 63% is worth knowing about if you live near it.
How often should I test my well in Portage County?
None of the 1 wells tested for bacteria in Portage 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 Portage County numbers come from
- People on wells: 33,322 in Portage County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 855 well water samples from 175 wells in the Water Quality Portal, run by the USGS and EPA, 2000 to 2025.
- Well depths: 7,756 Wisconsin drilling records for Portage County, gathered in the US Groundwater Well Database (Lin and others, 2024).
- Neighboring counties: the 6 counties that share a border with Portage 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 2 town water systems in Portage County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Portage County is zone 1 on the EPA Map of Radon Zones.
- State programs and links: Department of Natural Resources (DNR), checked November 1, 2026.