Manganese is widespread in Johnson County wells.
1 widespread, 4 rare out of 5 health checks.
From 22 wells tested in Johnson County since 2002; your own well needs its own test. How to read this
Not charted, because fewer than 10 wells were tested: uranium (6), 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 7 people 21,693 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 Johnson County compares with Iowa and the counties around it.
Each result puts Johnson County next to the 7 counties that border it, on the chart's 0 to 50% scale.
This one is widespread in Johnson County wells.
Manganese4 of 22 wells over
Too few tested to show: Cedar.
These 4 are rare in Johnson County.
Nitrate0 of 10 wells over
Too few tested to show: Cedar.
Arsenic0 of 22 wells over
Too few tested to show: Cedar.
Fluoride0 of 22 wells over
Too few tested to show: Cedar.
Lead0 of 22 wells over
Too few tested to show: Cedar.
Too few Johnson County wells were tested for these 2.
Uranium6 wells tested
Radon in water1 well tested
Coliform bacteria turned up in 1 of 7 tested Johnson County wells, so test for it every year.
Coliform bacteria1 of 7 wells had it
E. coli0 of 7 wells had it
E. coli means human or animal waste is getting in, so if a test of your Johnson County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 5 of 22 tested wells, and it isn't a health risk.
Iron stains5 of 22 wells had it
Too few tested to show: Cedar.
Most of the 22 wells tested in Johnson County were last tested before 2010.
An old result shows the water as it was then, so treat these 22 wells as a starting point and test your own.
Most Johnson 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 Johnson County.
- Bacteria
- Nitrate
- Manganese
- Arsenic
What Iowa offers well owners
- Free testingIowa's Private Well Grants program provides free testing for bacteria, nitrate, arsenic, and manganese through participating county environmental health offices. See the program
- Certified labsIowa's list of certified labs
- Well recordsIowa's well record search
Half the household wells here are shallower than 263 feet.
That comes from 1,540 household wells in Iowa's drilling records. Most wells of every kind here are 94 to 302 feet deep. Wells as deep as Johnson 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 82 of the 92 other Iowa counties with enough drilling records.
Look up your own well's depth in Iowa'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 Johnson County.
Johnson 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 5 town water systems in Johnson County test for PFAS. None found any. No well in Johnson 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 Johnson County
Is well water in Johnson County safe to drink?
4 of 22 wells tested in Johnson County had manganese over the limit, about 2 in 10. Across Iowa it's about 2 in 10. That's a bigger share than in 34 of the 67 other Iowa counties with 10 or more tested wells. So test your own well for manganese before you count on it.
Can I get my well tested for free in Johnson County?
Iowa's Private Well Grants program provides free testing for bacteria, nitrate, arsenic, and manganese through participating county environmental health offices. If not, use a lab Iowa has certified for drinking water. Ask for bacteria, nitrate, manganese and arsenic, the tests that matter most in Johnson County.
How deep are wells in Johnson County?
Half the household wells here are shallower than 263 feet. Typical household wells here go deeper than in 82 of the 92 other Iowa counties with enough drilling records.
How does Johnson County compare with the counties around it?
For manganese, the share of tested wells over the limit: 1 of the 6 neighboring counties with data had a higher share than Johnson County, at 18%. Linn had the most, at 38%. Groundwater doesn't stop at county lines, so Linn's 38% is worth knowing about if you live near it.
How often should I test my well in Johnson County?
In Johnson County, 1 of 7 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 Johnson County numbers come from
- People on wells: 21,693 in Johnson County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 210 well water samples from 22 wells in the Water Quality Portal, run by the USGS and EPA, 2002 to 2017.
- Well depths: 1,540 Iowa drilling records for Johnson County, gathered in the US Groundwater Well Database (Lin and others, 2024).
- Neighboring counties: the 7 counties that share a border with Johnson County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 5 town water systems in Johnson County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Johnson County is zone 1 on the EPA Map of Radon Zones.
- State programs and links: Iowa Department of Natural Resources, checked November 1, 2026.