Manganese is widespread in Franklin County wells.
1 widespread, 4 rare out of 5 health checks.
From 16 wells tested in Franklin County since 2000; your own well needs its own test. How to read this
Not charted, because fewer than 10 wells were tested: uranium (2), radon (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 2 people 48,621 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 Franklin County compares with Missouri and the counties around it.
Each result puts Franklin County next to the 7 counties that border it, on the chart's 0 to 50% scale.
This one is widespread in Franklin County wells.
Manganese7 of 16 wells over
Too few tested to show: Crawford, Gasconade, Jefferson, St. Louis, Warren, Washington.
These 4 are rare in Franklin County.
Arsenic0 of 16 wells over
Too few tested to show: Crawford, Gasconade, Jefferson, St. Louis, Warren, Washington.
Lead0 of 16 wells over
Too few tested to show: Crawford, Gasconade, Jefferson, St. Louis, Warren, Washington.
Nitrate0 of 16 wells over
Too few tested to show: Crawford, Gasconade, Jefferson, St. Louis, Warren, Washington.
Fluoride0 of 16 wells over
Too few tested to show: Crawford, Gasconade, Jefferson, St. Louis, Warren, Washington.
Too few Franklin County wells were tested for these 2.
Uranium2 wells tested
Radon in water2 wells tested
Coliform bacteria turned up in 1 of 2 tested Franklin County wells, so test for it every year.
Coliform bacteria1 of 2 wells had it
E. coli0 of 2 wells had it
E. coli means human or animal waste is getting in, so if a test of your Franklin County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 7 of 16 tested wells, and it isn't a health risk.
Iron stains7 of 16 wells had it
Too few tested to show: Crawford, Gasconade, Jefferson, St. Louis, Warren, Washington.
Most of the 16 wells tested in Franklin County were last tested before 2010.
An old result shows the water as it was then, so treat these 16 wells as a starting point and test your own.
Most Franklin 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 Franklin County.
- Bacteria
- Nitrate
- Manganese
- Arsenic
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 306 feet.
That comes from 7,478 household wells in Missouri's drilling records. Most wells of every kind here are 226 to 366 feet deep. Wells as deep as Franklin 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 go deeper than in 54 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 Franklin County.
Franklin 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 8 town water systems in Franklin 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 5.9 ng/L of PFOS. No well in Franklin 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 Franklin County
Is well water in Franklin County safe to drink?
7 of 16 wells tested in Franklin County had manganese over the limit, about 4 in 10. Across Missouri it's about 3 in 10. So test your own well for manganese before you count on it.
Can I get my well tested for free in Franklin 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, manganese and arsenic, the tests that matter most in Franklin County.
How deep are wells in Franklin County?
Half the household wells here are shallower than 306 feet. Typical household wells here go deeper than in 54 of the 105 other Missouri counties with enough drilling records.
How does Franklin County compare with the counties around it?
For manganese, the share of tested wells over the limit: St. Charles, the one neighbor with data, came in higher than Franklin County, at 47% against 44%. Groundwater doesn't stop at county lines, so St. Charles's 47% is worth knowing about if you live near it.
How often should I test my well in Franklin County?
In Franklin County, 1 of 2 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.
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Where the Franklin County numbers come from
- People on wells: 48,621 in Franklin County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 254 well water samples from 16 wells in the Water Quality Portal, run by the USGS and EPA, 2000 to 2016.
- Well depths: 7,478 Missouri drilling records for Franklin County, gathered in the US Groundwater Well Database (Lin and others, 2024).
- Neighboring counties: the 7 counties that share a border with Franklin County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 8 town water systems in Franklin County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Franklin 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.