Private wells
Iowa well water: who's on a well and what to test for
People on private wells
687,300
Homes on wells
21.1%
Est. above arsenic limit
35,700
Every Iowa county
Sorted by people on private wells. Arsenic and nitrate are modeled for typical wells in the county, not measured at yours; depth is the median of domestic well records.
| Johnson County | 21,700 | 13% | 10.9% | 0.4 | 220 ft |
| Pottawattamie County | 21,100 | 22% | 9.9% | 1.7 | 158 ft |
| Linn County | 21,000 | 9% | 5.1% | 0.6 | 220 ft |
| Polk County | 20,800 | 4% | 23.5% | 0.3 | 170 ft |
| Scott County | 19,000 | 10% | 15.0% | 0.6 | 200 ft |
| Dubuque County | 18,100 | 17% | 5.6% | 0.6 | 225 ft |
| Black Hawk County | 15,200 | 11% | 4.4% | 0.8 | 126 ft |
| Warren County | 13,600 | 26% | 16.4% | 1.7 | 45 ft |
| Clinton County | 13,300 | 27% | 11.0% | 0.9 | 150 ft |
| Woodbury County | 12,500 | 12% | 22.4% | 1.6 | 155 ft |
| Story County | 12,500 | 13% | 34.6% | 0.1 | 177 ft |
| Marion County | 11,300 | 32% | 12.4% | 0.9 | 135 ft |
| Dallas County | 11,100 | 10% | 21.3% | 0.8 | 75 ft |
| Lee County | 10,900 | 32% | 10.1% | 0.3 | 104 ft |
| Buchanan County | 10,400 | 48% | 4.9% | 0.4 | 160 ft |
| Bremer County | 10,200 | 37% | 6.1% | 0.9 | 127 ft |
| Benton County | 9,600 | 36% | 8.2% | 0.3 | 246 ft |
| Delaware County | 9,400 | 53% | 8.3% | 0.8 | 165 ft |
| Muscatine County | 9,300 | 21% | 8.4% | 0.8 | 135 ft |
| Winneshiek County | 9,300 | 47% | 4.4% | 0.7 | 280 ft |
| Jones County | 9,200 | 44% | 9.6% | 1.1 | 181 ft |
| Clayton County | 9,000 | 51% | 7.4% | 0.6 | 208 ft |
| Plymouth County | 8,900 | 33% | 11.7% | 2.5 | 185 ft |
| Cerro Gordo County | 8,600 | 18% | 6.1% | 0.2 | 150 ft |
| Webster County | 8,600 | 21% | 11.2% | 0.0 | 185 ft |
| Jasper County | 8,600 | 23% | 16.1% | 0.6 | 200 ft |
| Washington County | 8,500 | 36% | 9.8% | 0.1 | 150 ft |
| Jackson County | 8,400 | 43% | 7.5% | 1.0 | 200 ft |
| Fayette County | 7,900 | 37% | 2.5% | 0.6 | 150 ft |
| Sioux County | 7,900 | 22% | 26.5% | 1.9 | 176 ft |
| Des Moines County | 7,800 | 18% | 9.1% | 0.1 | 120 ft |
| Madison County | 7,600 | 43% | 8.3% | 1.7 | 44 ft |
| Harrison County | 7,600 | 49% | 8.7% | 1.1 | 150 ft |
| Cedar County | 7,400 | 38% | 10.2% | 0.7 | 165 ft |
| Boone County | 7,100 | 25% | 11.3% | 0.1 | 137 ft |
| Tama County | 7,100 | 41% | 10.5% | 0.5 | 200 ft |
| Davis County | 7,100 | 77% | 6.9% | 1.6 | 77 ft |
| Henry County | 7,000 | 30% | 10.1% | 0.1 | 170 ft |
| Allamakee County | 6,900 | 53% | 5.5% | 0.6 | 250 ft |
| Mills County | 6,900 | 46% | 6.5% | 1.4 | 100 ft |
| Wapello County | 6,700 | 18% | 12.9% | 0.4 | 105 ft |
| Lucas County | 6,600 | 75% | 10.1% | 1.9 | n/a |
| Iowa County | 6,600 | 38% | 13.4% | 0.3 | 175 ft |
| Floyd County | 6,400 | 37% | 5.3% | 0.3 | 160 ft |
| Butler County | 6,200 | 42% | 4.4% | 0.6 | 141 ft |
| Mahaska County | 6,100 | 27% | 7.5% | 0.2 | 180 ft |
| Poweshiek County | 5,800 | 33% | 16.9% | 0.3 | 219 ft |
| Van Buren County | 5,800 | 80% | 7.4% | 0.8 | 80 ft |
| Chickasaw County | 5,800 | 45% | 8.5% | 0.2 | 130 ft |
| Marshall County | 5,800 | 15% | 23.1% | 0.3 | 210 ft |
| Hardin County | 5,500 | 32% | 11.6% | 0.2 | 140 ft |
| Monroe County | 5,500 | 72% | 6.7% | 1.8 | 117 ft |
| Buena Vista County | 5,200 | 28% | 36.2% | 0.3 | 160 ft |
| Lyon County | 5,200 | 40% | 38.1% | 2.4 | 115 ft |
| Louisa County | 5,100 | 49% | 6.5% | 0.4 | 110 ft |
| Kossuth County | 5,100 | 32% | 32.1% | 0.0 | 183 ft |
| Carroll County | 5,100 | 22% | 9.8% | 0.9 | 140 ft |
| Wayne County | 5,000 | 74% | 14.3% | 1.1 | 57 ft |
| Appanoose County | 4,800 | 37% | 9.3% | 1.3 | 60 ft |
| Grundy County | 4,700 | 36% | 15.3% | 0.2 | 200 ft |
| Clay County | 4,700 | 27% | 61.9% | 0.4 | 65 ft |
| Mitchell County | 4,700 | 41% | 4.5% | 0.4 | 115 ft |
| Sac County | 4,700 | 47% | 27.3% | 1.1 | 132 ft |
| Jefferson County | 4,700 | 27% | 12.9% | 0.9 | 50 ft |
| Guthrie County | 4,700 | 44% | 8.2% | 1.4 | 98 ft |
| Keokuk County | 4,700 | 44% | 11.6% | 0.3 | 180 ft |
| Shelby County | 4,600 | 38% | 4.7% | 3.0 | 48 ft |
| Crawford County | 4,500 | 29% | 4.0% | 5.2 | 50 ft |
| Hamilton County | 4,300 | 28% | 12.0% | 0.0 | 190 ft |
| Franklin County | 4,300 | 44% | 25.7% | 0.1 | 110 ft |
| Howard County | 4,200 | 40% | 6.3% | 0.5 | 150 ft |
| Clarke County | 3,900 | 40% | 12.1% | 1.6 | 68 ft |
| Cass County | 3,800 | 28% | 8.1% | 1.3 | 139 ft |
| Hancock County | 3,800 | 34% | 11.4% | 0.1 | 140 ft |
| Decatur County | 3,600 | 43% | 6.8% | 1.5 | 45 ft |
| Cherokee County | 3,600 | 29% | 29.9% | 2.7 | 210 ft |
| Dickinson County | 3,500 | 18% | 33.7% | 0.3 | 89 ft |
| Calhoun County | 3,500 | 36% | 15.9% | 0.0 | 150 ft |
| Monona County | 3,500 | 40% | 12.1% | 2.2 | 100 ft |
| Worth County | 3,400 | 44% | 6.5% | 0.1 | 111 ft |
| Winnebago County | 3,400 | 32% | 16.3% | 0.0 | 155 ft |
| Page County | 3,400 | 22% | 6.2% | 4.0 | 48 ft |
| Taylor County | 3,300 | 56% | 4.4% | 1.8 | 50 ft |
| O'Brien County | 3,300 | 22% | 33.1% | 1.3 | 65 ft |
| Adair County | 3,300 | 43% | 6.3% | 2.4 | 35 ft |
| Ida County | 3,300 | 45% | 8.1% | 3.6 | 175 ft |
| Humboldt County | 3,300 | 33% | 13.3% | 0.0 | 150 ft |
| Greene County | 3,000 | 34% | 8.6% | 0.1 | 140 ft |
| Wright County | 2,900 | 23% | 11.1% | 0.0 | 150 ft |
| Union County | 2,700 | 21% | 6.6% | 1.5 | 37 ft |
| Audubon County | 2,700 | 45% | 9.6% | 3.4 | 35 ft |
| Fremont County | 2,600 | 39% | 8.9% | 2.3 | 80 ft |
| Montgomery County | 2,500 | 23% | 6.4% | 1.7 | 100 ft |
| Pocahontas County | 2,500 | 33% | 16.8% | 0.0 | 155 ft |
| Palo Alto County | 2,400 | 27% | 33.8% | 0.1 | 160 ft |
| Osceola County | 2,300 | 35% | 32.6% | 0.7 | 88 ft |
| Emmet County | 2,300 | 25% | 33.0% | 0.1 | 218 ft |
| Ringgold County | 2,100 | 45% | 5.3% | 2.3 | 56 ft |
| Adams County | 1,800 | 46% | 6.7% | 1.1 | 45 ft |
Shading: red is among the highest counties nationally, amber the middle, green the lower range. Click a column to sort.
Most well users above the arsenic limit
- Kossuth County: about 1,700 people
- Webster County: about 1,500 people
- Boone County: about 1,500 people
- Hancock County: about 1,400 people
- Dallas County: about 970 people
Highest modeled nitrate
- Crawford County: 5.2 mg/L average (limit 10)
- Page County: 4.0 mg/L average (limit 10)
- Ida County: 3.6 mg/L average (limit 10)
- Audubon County: 3.4 mg/L average (limit 10)
Test first, then treat what the test finds
We may earn a commission from links below, at no cost to you. Picks follow the testing order, not who pays. How we make money.
1. Certified lab well test
Start here, every year
A mail-in kit analyzed by a certified lab measures bacteria, nitrate, arsenic, metals and more. Test strips cannot measure arsenic or uranium reliably.
Mail-in certified lab well water test
Mid-range2. Sediment pre-filter
Sand, silt or cloudy water
A 5-micron cartridge after the pressure tank catches sand, silt and rust before they reach fixtures or other filters. Cartridges are cheap and swap every few months.
5-micron whole-house sediment filter
Budget3. Iron and sulfur filter
Orange stains or rotten-egg smell
Air-injection or oxidizing-media filters remove orange staining and rotten-egg smell. Size one from a lab result for iron, manganese and hydrogen sulfide.
Air-injection iron and sulfur filter
Premium4. UV disinfection system
Coliform bacteria in a test
Inactivates bacteria and viruses; usually for private wells or after boil notices.
12 GPM whole-house UV purifier
Premium5. Under-sink reverse osmosis
Arsenic, nitrate or uranium in a test
The most thorough option for drinking water: PFAS, lead, nitrate, arsenic and more. Look for NSF/ANSI 58.
Waterdrop G3P600 tankless RO
Price at Waterdrop, checked Oct 5, 2026or compare on Amazon
iSpring RCC7AK reverse osmosis
Mid-range6. Whole-house well filter
Several problems at once
Multi-stage sediment and carbon for every tap. Add UV if bacteria shows up, and choose stages from your lab results, not a guess.
Waterdrop WHF21-PG 2-stage whole-house filter
Price at Waterdrop, checked Oct 5, 2026
Questions
Which Iowa counties rely most on wells?+
By share of homes: Van Buren County (80%), Davis County (77%), Lucas County (75%), Wayne County (74%), Monroe County (72%). By number of people: Johnson County (21,700), Pottawattamie County (21,100), Linn County (21,000).
Is arsenic a problem in Iowa wells?+
USGS estimates about 35,700 Iowa well users have water above the 10 microgram per liter arsenic limit that applies to public systems, the largest numbers in Kossuth County, Webster County, Boone County. Arsenic has no taste or smell, so only a lab test finds it.
Do I have to test my well when I sell a house in Iowa?+
We could not confirm a statewide rule for Iowa. Check with your county health department. Buyers can still make a lab test a condition of the offer.
How often should I test my well?+
No federal law covers private wells. EPA's drinking water limits apply to public water systems, so testing and treating a private well is up to the owner. EPA and CDC recommend testing at least once a year for coliform bacteria, nitrate, pH and total dissolved solids, and testing for arsenic, uranium, radon and other local concerns based on where you live.
Well-user counts, arsenic and nitrate figures are each a modeled estimate built from national datasets, not a count of tested wells, and well depths summarize drilling records rather than every well. Your own well can be very different from the county average, which is why the only answer for your home is a lab test. Sources: EPA Office of Research and Development, Water Source 2020 (private well estimates by census block); CDC Environmental Public Health Tracking, Well Water Index (from USGS nitrate and arsenic models); USGS, county-level domestic well population with arsenic above 10 micrograms per liter (Ayotte and others, 2017); USGS Synthesized Domestic Well Database for the Conterminous United States (SynDWell-US), McCarthy and others, 2025 (depth, where a county has 30+ usable records).