Well water in Winnebago County, Iowa
1in5
Testing strongly recommended
tested well samples in Winnebago County exceeded the EPA limit for radium (226 + 228) (5 pCi/L), based on public data from USGS Water Quality Portal.
661 test results across 13 contaminants from at least 21 wells, 1934 to 2014; chloride has the most at 81. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
An estimated 2,853 people in Winnebago County get their drinking water from a private well, per USGS 2015 county water use. That is about 27% of residents.
Separately, the USGS national arsenic model estimates that 18% of the 2,853 people on private wells in Winnebago County draw water above 10 ug/L (the model's range is 14% to 23%), from geology and well depth rather than local tests.
What individual samples found
Each row summarizes every public sample for that contaminant inside Winnebago County. Above limit means above the EPA maximum contaminant level; where EPA has no enforceable limit, the row shows a health guideline or nuisance level instead.
| Contaminant | Above limit | Samples | Detected | Median | Highest | Limit |
|---|---|---|---|---|---|---|
| Radium (226 + 228) 1971 to 2014 | 74 | 80% | 2.75 | 8 | 5 pCi/L EPA limit | |
| Nitrate 1934 to 2014 | 76 | 36% | 0 | 1.7 | 10 mg/L EPA limit | |
| Fluoride 1934 to 2014 | 72 | 100% | 0.32 | 1 | 4 mg/L EPA limit | |
| Copper 1971 to 2014 | 44 | 18% | 0 | 0.04 | 1.3 mg/L EPA limit | |
| Lead 1971 to 2014 | 44 | 2% | 0 | 0.169 | 15 ug/L EPA limit | |
| Arsenic 1971 to 2014 | 44 | 18% | 0 | 7 | 10 ug/L EPA limit | |
| Chloride 1934 to 2014 | no limit | 81 | 65% | 1 | 5.8 | 250 mg/L nuisance level |
| Sodium 1956 to 2014 | no limit | 72 | 100% | 19 | 170 | 20 mg/L health guideline |
| Iron 1934 to 2014 | no limit | 70 | 99% | 1,280 | 12,000 | 300 ug/L nuisance level |
| Manganese 1934 to 2014 | no limit | 69 | 87% | 50 | 260 | 300 ug/L health guideline |
| Radon 1982 to 2014 | no limit | 11 | 100% | 460 | 1,530 | 2,000 pCi/L health guideline |
Sampled fewer than 10 times, too few to summarize: Uranium (3), E. coli (1).
Over time
Share of samples above the limit by period. A cell needs ten samples to show; a comparison needs twenty in each period. Later periods sample fewer wells, and often the ones already known to have a problem.
| Contaminant | before 2000 | 2000s | 2010s | 2020s |
|---|---|---|---|---|
| Radium (226 + 228) | 19%26 samples | 20%44 samples | n/a | n/a |
| Fluoride | 0%59 samples | 0%11 samples | n/a | n/a |
Radium (226 + 228) has held within a few points between the two most recent periods with enough samples.
Closer than the county
See the sampled wells near your address
The same records, drawn around one point: which wells within a few miles were sampled and what they found, how deep the wells next to you were drilled, and any leaking tank or cleanup site within a mile.
Check my addressWhat this means
The contaminants most often above their limit here are radium (226 + 228) (20% of 74 samples). A well next door can differ sharply from yours because bedrock fractures, well depth and plumbing all matter, so these rates describe the area, not your tap.
Chloride, Iron, and Manganese are widespread in local groundwater. They are mainly a staining and taste problem, but high manganese also carries a health advisory for infants.
What to test for in Winnebago County
- 1Radium (226 + 228)20% of 74 local samples were above the limit.
- 2Coliform bacteriaRecommended for every private well, every year.
- 3RadonMedian local reading is 460 pCi/L.
- 4NitrateRecommended for every private well, especially near farms or septic systems.
- 5FluorideDetected in 100% of local samples.
- 6IronDetected in 99% of local samples.
- 7ManganeseDetected in 87% of local samples.
- 8Volatile organic compounds (VOCs)32 leaking underground storage tank sites on record locally.
- 9Metals panel3 hazardous waste sites on record locally.
Test your Winnebago County well for radium (226 + 228), coliform bacteria and radon
Certified lab analysis of your own tap water, bottles and prepaid return shipping included. The Essential well panel covers arsenic, uranium, nitrate, lead, copper, manganese, iron, sodium and bacteria; radon and PFAS are add-ons.
Order the Tap Score well water test kit, from $209Already tested? Upload the report
Just want bacteria checked first? Tap Score coliform and E. coli test, $99. Coliform and E. coli are the tests every well needs every year.
Want a quick look before paying for a lab? Home well water test strips on Amazon check hardness, iron, pH and nitrate in minutes. They are a screen, not a result: arsenic, bacteria, uranium and PFAS need a certified lab.
Affiliate links: the merchant pays us a commission and the price is the same for you. It does not change what the data above says. As an Amazon Associate we earn from qualifying purchases.
Where to get a well tested in Iowa: certified labs, state programs and prices.
Already have results back? Get your lab report read against the Winnebago County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
The rock under Winnebago County
Upper carbonate aquifer
Carbonate-rock. Limestone and dolomite move water through cracks and solution channels, sometimes very fast. Bacteria and nitrate can travel from the surface to a well in days, so annual bacteria testing matters more here than most places; hardness is a given.
Classification from the USGS Principal Aquifers of the United States (national map, 2003 edition, GIS release 2015), read at the county centroid. A single well can sit in a different unit, especially near a boundary.
Official help in Iowa
Two places to start that are not selling anything: the state program that answers private well questions, and its list of labs certified to run drinking water tests. A certified lab is the difference between a result you can act on and a number.
- Private Well Program, Iowa DNR
- LabCert - List of Certified Labs, Iowa DNR
Contamination sources on record in Winnebago County
Iowa DNR records 32 leaking underground storage tank sites and 3 hazardous waste sites in Winnebago County, among 58 regulated sites in total. Groundwater does not follow property lines, so a well within a few hundred feet of one of these is worth testing for what that site could release.
- 32
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 3
- hazardous waste sitesSolvents, degreasers and metals from industrial sites can travel far in fractured bedrock.
- 1
- lined landfill or transfer facility
- 9
- other remediation projects
- 13
- other solid waste facilities
Treatment that fits the local profile
Radium (226 + 228)
Water softener (cation exchange); Point-of-use reverse osmosis
Iron
Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration
Manganese
Oxidizing filter (greensand, birm) whole-house; Water softener (low levels); Point-of-use reverse osmosis
Systems we would look at first
Some links below are affiliate links. If you buy through one, the merchant pays us a commission at no extra cost to you. It does not change which products we list or what the data says.
For radium (226 + 228)
Under-sink reverse osmosis system
under-sink or countertop, about $300
Look for NSF/ANSI 58 certification listing the contaminant you need removed.
For iron
Iron and manganese oxidizing filter
whole-house, at the point of entry, about $1,800
Air-injection or greensand media; fixes staining at the source.
Free, no obligation
Get on the list for a free in-home water test in Winnebago County
No water treatment company serves Winnebago County through Well Water Nerd yet. We are signing licensed companies on county by county: they test at your tap for free, walk you through the numbers, and quote treatment only if something needs fixing. Leave your details and you are first in line. Nothing is shared until a company joins for Winnebago County, and you get an email naming it first.
Common questions
Is there arsenic in well water in Winnebago County?
Arsenic was detected in 18% of 44 public well samples in Winnebago County, and 0% were above the EPA limit of 10 ug/L. Arsenic has no taste or smell; a lab test is the only way to know your level.
How high is radon in well water in Winnebago County?
The median radon level across 11 public samples in Winnebago County was 460 pCi/L, with a high of 1,530 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Winnebago County?
Test for bacteria and nitrate every year. Test once for arsenic, uranium, radon, fluoride, manganese and PFAS, then again every three to five years or after any change in taste, color, or plumbing.
Counties near Winnebago County
Closest first. Groundwater does not stop at a line on a map, so the next county over is a fair second opinion.
Want the numbers themselves? Download the Iowa dataset as CSV, every county and town, with the sources named.
Sources
- USGS Water Quality Portal: 661 samples in Winnebago County. Data from the Water Quality Portal, a service of USGS, EPA and USDA; groundwater samples collected by USGS and cooperators. Retrieved September 3, 2026.
- USGS national arsenic model (Ayotte 2017): estimated share of 2,853 people on private wells in Winnebago County above 10 ug/L of arsenic, from geology, well depth and land use. County estimates of domestic well users with arsenic above 10 ug/L from the USGS national logistic regression model (Ayotte, Medalie and Qi, 2017), with private well population from the USGS 2015 county water-use compilation (Dieter and others, 2018). Retrieved September 15, 2026.
- Iowa DNR regulated sites: 58 regulated sites located in Winnebago County. Contaminated sites, solid waste facilities and leaking underground storage tank sites from the Iowa Department of Natural Resources. Retrieved September 18, 2026.
Non-detects count as samples and are treated as zero when computing medians. Exactly at the limit counts as not above it. A sample belongs to the town containing the well's reported coordinates.