Manganese and nitrate are widespread in Madison County wells.
2 widespread, 4 rare out of 6 health checks.
From 13 wells tested in Madison County since 2001; your own well needs its own test. How to read this
Rare: under 5%Worth checking: 5 to 15%Widespread: 15%+
Lab results: Water Quality Portal (USGS and EPA)
Who drinks from a well here
About 1 in 13 people 20,124 people
Nobody else tests these wells. Only you do.
People on wells: EPA researchers' 2020 estimate
How deep wells go here
Shallow wells: watch for fertilizer and germs from above.
Well depths: US Groundwater Well Database
Radon risk (a gas from rock)
Possible here. A home air test is inexpensive.
Radon zones: EPA map
Here's how Madison County compares with Illinois and the counties around it.
Each result puts Madison County next to the 9 counties that border it, on the chart's 0 to 50% scale.
These 2 are widespread in Madison County wells.
Manganese5 of 11 wells over
Too few tested to show: Bond, Clinton, Jersey, Macoupin, Montgomery, St. Clair, St. Louis city, MO, St. Louis, MO.
Nitrate2 of 12 wells over
Too few tested to show: Bond, Clinton, Jersey, Macoupin, Montgomery, St. Louis city, MO, St. Louis, MO.
These 4 are rare in Madison County.
Arsenic0 of 11 wells over
Too few tested to show: Bond, Clinton, Jersey, Macoupin, Montgomery, St. Clair, St. Louis city, MO, St. Louis, MO.
Lead0 of 11 wells over
Too few tested to show: Bond, Clinton, Jersey, Macoupin, Montgomery, St. Clair, St. Louis city, MO, St. Louis, MO.
Fluoride0 of 11 wells over
Too few tested to show: Bond, Clinton, Jersey, Macoupin, Montgomery, St. Clair, St. Louis city, MO, St. Louis, MO.
Uranium0 of 11 wells over
Too few tested to show: Bond, Clinton, Jersey, Macoupin, Montgomery, St. Clair, St. Louis city, MO, St. Louis, MO.
Every well needs a bacteria test every year.
No bacteria tests from Madison County wells are in the public data. Test every year anyway.
Iron reached staining levels in 5 of 11 tested wells, and it isn't a health risk.
Iron stains5 of 11 wells had it
Too few tested to show: Bond, Clinton, Jersey, Macoupin, Montgomery, St. Clair, St. Louis city, MO, St. Louis, MO.
Madison County has 13 tested wells, and the busiest decade for testing was the 2000s.
Only 1 of the 13 wells have a test from 2020 or later, so a fresh test of your own well tells you more than any of these.
Most Madison 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 4 things to check in Madison County.
- Bacteria
- Nitrate
- Manganese
- Arsenic
What Illinois offers well owners
- Free testingWe didn't find a free program for all of Illinois. Illinois's private well page
- Certified labsIllinois's list of certified labs
- Well recordsIllinois's well record search
Half the household wells here are shallower than 40 feet.
That comes from 3,178 household wells in Illinois's drilling records. Most wells of every kind here are 35 to 69 feet deep. Wells as shallow as Madison County's pick up bacteria and nitrate from the surface more easily, so the yearly test matters even more here. Typical household wells here are shallower than in 93 of the 101 other Illinois counties with enough drilling records.
Look up your own well's depth in Illinois'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 Madison County.
Madison 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 19 town water systems in Madison County test for PFAS. 4 of them had at least one test above 4 ng/L, the new EPA limit for PFOA and PFOS. The highest single result was 18 ng/L of PFOA. No well in Madison 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 Madison County
Is well water in Madison County safe to drink?
5 of 11 wells tested in Madison County had manganese over the limit, about 5 in 10. Across Illinois it's about 1 in 8. That's the highest share among the 7 Illinois counties with 10 or more tested wells. So test your own well for manganese before you count on it.
Where can I get my well tested in Madison County?
Use a lab Illinois has certified for drinking water. Illinois's list is linked above, in the box about testing. Ask for bacteria, nitrate, manganese and arsenic, the tests that matter most in Madison County.
How deep are wells in Madison County?
Half the household wells here are shallower than 40 feet. Typical household wells here are shallower than in 93 of the 101 other Illinois counties with enough drilling records.
How does Madison County compare with the counties around it?
For manganese, the share of tested wells over the limit: St. Charles, MO, the one neighbor with data, came in higher than Madison County, at 47% against 45%. Groundwater doesn't stop at county lines, so St. Charles, MO's 47% is worth knowing about if you live near it.
How often should I test my well in Madison County?
Madison 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.
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Where the Madison County numbers come from
- People on wells: 20,124 in Madison County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 207 well water samples from 13 wells in the Water Quality Portal, run by the USGS and EPA, 2001 to 2023.
- Well depths: 3,178 Illinois drilling records for Madison County, gathered in the US Groundwater Well Database (Lin and others, 2024).
- Neighboring counties: the 9 counties that share a border with Madison County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 19 town water systems in Madison County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Madison County is zone 2 on the EPA Map of Radon Zones.
- State programs and links: Illinois Department of Public Health, checked November 1, 2026.