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Nitrate in Iowa well water, by county

By the Tested Water teamLab data from the USGS and EPA Water Quality Portal, 2000 to 2023Updated November 8, 2026

Nitrate is widespread, over the limit in 15% or more of tested wells, in 10 of the 38 Iowa counties with 10 or more tested wells. A county's share tells you how likely a problem is nearby. Only a test of your own well tells you what's in it.

Find a nitrate test See every county

How Iowa compares with the rest of the country

Across Iowa, about 1 in 12 tested wells had nitrate over the EPA limit of 10 mg/L (80 of 932). Across all tested wells in the US it's about 1 in 12. Iowa is about average, so the county you live in tells you more than the state does.

Why it matters: It's dangerous for babies under 6 months, because it keeps their blood from carrying enough oxygen.

Nitrate soaks down into groundwater from fertilizer, manure and septic systems.

Nitrate in tested wells, county by county

Share of each county's tested wells with at least one result over the EPA limit of 10 mg/L. Counties need 10 or more tested wells to be listed. Widespread means 15% or more, worth checking 5 to 15%, rare under 5%.

CountyWells testedWells over the limitLevel
Sioux County 12
33% 4 of 12
 Widespread
Floyd County 19
32% 6 of 19
 Widespread
Plymouth County 16
31% 5 of 16
 Widespread
Monona County 13
31% 4 of 13
 Widespread
Woodbury County 18
22% 4 of 18
 Widespread
Butler County 10
20% 2 of 10
 Widespread
Mitchell County 29
17% 5 of 29
 Widespread
Black Hawk County 12
17% 2 of 12
 Widespread
Pottawattamie County 12
17% 2 of 12
 Widespread
Benton County 13
15% 2 of 13
 Widespread
Hardin County 42
12%* 5 of 42
 Worth checking
Louisa County 10
10% 1 of 10
 Worth checking
Linn County 51
10% 5 of 51
 Worth checking
Muscatine County 22
9% 2 of 22
 Worth checking
Fayette County 11
9% 1 of 11
 Worth checking
Hamilton County 49
8% 4 of 49
 Worth checking
Hancock County 13
8% 1 of 13
 Worth checking
Iowa County 14
7% 1 of 14
 Worth checking
Webster County 20
5% 1 of 20
 Worth checking
Jackson County 23
4% 1 of 23
 Rare
Jasper County 27
4% 1 of 27
 Rare
Dallas County 22
0% 0 of 22
 Rare
Carroll County 15
0% 0 of 15
 Rare
Story County 14
0% 0 of 14
 Rare
Tama County 14
0% 0 of 14
 Rare
O'Brien County 13
0% 0 of 13
 Rare
Winneshiek County 13
0% 0 of 13
 Rare
Buena Vista County 12
0% 0 of 12
 Rare
Cherokee County 12
0% 0 of 12
 Rare
Clayton County 12
0% 0 of 12
 Rare
Mills County 12
0% 0 of 12
 Rare
Clinton County 11
0% 0 of 11
 Rare
Guthrie County 10
0% 0 of 10
 Rare
Harrison County 10
0% 0 of 10
 Rare
Johnson County 10
0% 0 of 10
 Rare
Marshall County 10
0% 0 of 10
 Rare
Polk County 10
0% 0 of 10
 Rare
Washington County 10
0% 0 of 10
 Rare

* Likely overstated. These shares come from a narrow set of wells, so they probably run high for the county as a whole:

  • Hardin County: All of these tests come from the US Geological Survey between 2002 and 2009 in one small part of the county, so this likely overstates it.

52 more Iowa counties have 1 to 9 tested wells for nitrate, too few to rate.

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Where to get your well tested for nitrate in Iowa

1

Free state testing

Iowa tests private wells for bacteria, nitrate, arsenic and manganese for free through participating county health offices. Check which tests it includes before you count on it for nitrate.

Iowa's private well page
2

A lab Iowa certifies

Ask for nitrate by name. Results from a certified lab count for a home sale or a loan.

Labs certified by Iowa
3

A mail-in kit

Fill the bottles at your kitchen tap and mail them back. We mark the kits that include nitrate.

Compare kits

Keep reading about wells in Iowa

Questions people ask about nitrate in Iowa

Is there nitrate in Iowa well water?

Nitrate is widespread, over the limit in 15% or more of tested wells, in 10 of the 38 Iowa counties with 10 or more tested wells. Across Iowa, about 1 in 12 tested wells had nitrate over the EPA limit of 10 mg/L (80 of 932). Across all tested wells in the US it's about 1 in 12. Iowa is about average, so the county you live in tells you more than the state does.

Where can I get my well tested for nitrate in Iowa?

Iowa tests private wells for bacteria, nitrate, arsenic and manganese for free through participating county health offices. If that doesn't cover you, use a lab certified by Iowa for drinking water, or a mail-in kit that includes nitrate from a certified lab.

See Iowa's list of certified labs, or compare mail-in kits.

Where these numbers come from

  • Lab tests: Water Quality Portal (USGS and EPA), well samples since 2000. A well counts as over if any of its tests was over the EPA limit of 10 mg/L. Wells tested for studies and monitoring, not a random sample of homes.
  • Likely overstated: our own check of who tested the wells, when and where. How we check.
  • State programs and links: Iowa Department of Natural Resources.