Arsenic has turned up often in St. Francois County wells, mostly in older study samples.
1 likely overstated, 1 worth checking, 3 rare out of 5 health checks.
From 27 wells tested in St. Francois County since 2004; your own well needs its own test. How to read this
*Arsenic and manganese: All of these tests come from the US Geological Survey between 2004 and 2007 in one small part of the county, so this likely overstates them.
Not charted, because fewer than 10 wells were tested: uranium (2).
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 3 people 20,594 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)
Possible here. A home air test is inexpensive.
Radon zones: EPA map
Here's how St. Francois County compares with Missouri and the counties around it.
Each result puts St. Francois 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 older study samples.
Arsenic15 of 27 wells over
All of these tests come from the US Geological Survey between 2004 and 2007 in one small part of the county, so this likely overstates it.
This one is worth checking in St. Francois County.
Manganese3 of 27 wells over
All of these tests come from the US Geological Survey between 2004 and 2007 in one small part of the county, so this likely overstates it.
These 3 are rare in St. Francois County.
Lead1 of 27 wells over
Nitrate0 of 27 wells over
Fluoride0 of 27 wells over
Too few St. Francois County wells were tested for this one.
Uranium2 wells tested
Every well needs a bacteria test every year.
No bacteria tests from St. Francois County wells are in the public data. Test every year anyway.
Iron reached staining levels in 11 of 27 tested wells, and it isn't a health risk.
Iron stains11 of 27 wells had it
Most of the 27 wells tested in St. Francois County were last tested before 2010.
An old result shows the water as it was then, so treat these 27 wells as a starting point and test your own.
Most St. Francois 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 St. Francois County.
- Bacteria
- Nitrate
- Arsenic
- Manganese
What Missouri offers well owners
- Free testingThe State Public Health Laboratory tests private well water for bacteria for a $10 handling fee, with kits available through local public health agencies. See the program
- Certified labsMissouri's list of certified labs
- Well recordsMissouri's well record search
Half the household wells here are shallower than 287 feet.
That comes from 4,151 household wells in Missouri's drilling records. Most wells of every kind here are 123 to 345 feet deep. Wells as deep as St. Francois 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 58 of the 105 other Missouri counties with enough drilling records.
Look up your own well's depth in Missouri'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 St. Francois County.
St. Francois 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 6 town water systems in St. Francois County test for PFAS. 1 found some PFAS, all below the new limits. No well in St. Francois 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 St. Francois County
Is well water in St. Francois County safe to drink?
15 of 27 wells tested in St. Francois County had arsenic over the limit, about 6 in 10. Across Missouri it's about 2 in 10. We don't rank this against other Missouri counties, because most of these tests are old study samples. All of these tests come from the US Geological Survey between 2004 and 2007 in one small part of the county, so this likely overstates it. So test your own well for arsenic before you count on it.
Can I get my well tested for free in St. Francois County?
The State Public Health Laboratory tests private well water for bacteria for a $10 handling fee, with kits available through local public health agencies. If not, use a lab Missouri has certified for drinking water. Ask for bacteria, nitrate, arsenic and manganese, the tests that matter most in St. Francois County.
How deep are wells in St. Francois County?
Half the household wells here are shallower than 287 feet. Typical household wells here are shallower than in 58 of the 105 other Missouri counties with enough drilling records.
How often should I test my well in St. Francois County?
St. Francois 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 St. Francois County numbers come from
- People on wells: 20,594 in St. Francois County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 344 well water samples from 27 wells in the Water Quality Portal, run by the USGS and EPA, 2004 to 2007.
- Well depths: 4,151 Missouri drilling records for St. Francois County, gathered in the US Groundwater Well Database (Lin and others, 2024).
- Neighboring counties: the 6 counties that share a border with St. Francois County, from the Census Bureau's county adjacency file.
- Results marked likely overstated: our own check of who tested the wells, when and where.
- PFAS: EPA tests of 6 town water systems in St. Francois County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: St. Francois County is zone 2 on the EPA Map of Radon Zones.
- State programs and links: Missouri Department of Health and Senior Services, checked November 1, 2026.