The water in a private well can look clear and still carry a farm chemical. In Iowa, the strongest documented private-well evidence is for nitrate and pesticides, including atrazine. PFAS from sewage sludge spread on farmland is another possible route into groundwater, but Iowa’s public well data do not establish that sludge has contaminated a particular household well. Those are different claims, and families deserve to know the difference.
What Iowa’s well tests actually show
The Iowa Department of Health and Human Services’ private-well tracker reports nitrate tests, the number at or above 10 milligrams per liter, and the share of elevated tests. Its underlying records come from the Iowa Department of Natural Resources’ Private Well Tracking System, much of it through county health departments. The state’s explanation of the data matters as much as the map: only wells that were tested appear, and one sample per well cannot show a long-term trend or identify the source of pollution at that address.
An Iowa Environmental Council and Environmental Working Group analysis of DNR records found that, among nearly 55,000 wells tested for nitrate from 2002 through 2017 (excluding 2014 because of data problems), more than 6,600 averaged at or above 10 mg/L. More than 12,300 averaged at or above 5 mg/L. The federal 10 mg/L limit applies to public drinking-water systems; private wells do not have the same routine compliance program. These figures describe tested wells, not the share of every Iowa well that is unsafe today.
The county picture is uneven. The state tracker provides county-level results, while the DNR-based county map shows where testing found nitrate and bacteria from 2002 through 2017. Eight counties had 10 or fewer wells tested for nitrate or bacteria in that period, according to the Council’s analysis. A lightly marked county can therefore mean too little testing, not clean groundwater. The Council’s 2026 review of Iowa well records identifies western Iowa and northeast Iowa’s karst region as areas where nitrate contamination is especially evident. Karst’s fractured rock can move surface pollution into groundwater quickly. The DNR warns that shallow wells and shallow karst aquifers are particularly vulnerable.
Where manure and fertilizer enter the story
Nitrate can come from several sources, including septic systems. But in farm country, nitrogen from synthetic fertilizer and livestock manure can pass through soil into an aquifer. USDA’s Economic Research Service describes both as groundwater nitrate sources. The Iowa Environmental Council’s 2026 report says manure and fertilizer are the main agricultural inputs behind Iowa’s nonpoint nitrate pollution.
That connection is measurable without pretending every contaminated well has one known culprit. A peer-reviewed Iowa study summarized by the U.S. Geological Survey found a significant positive association between the number of animal feeding operations within two kilometers of a private well and its groundwater nitrate. Another study cited by the Iowa Environmental Council found that distance to the nearest feeding operation, well depth, nearby slope length, and sampling year were among the strongest predictors of high nitrate. Those studies show a pattern around concentrated livestock production; a sample and site investigation are still needed to assess an individual well.
Atrazine is in the record, too
Pesticide application leaves a separate fingerprint. In an Iowa DNR study of private wells in communities without public water, atrazine was detected in 19% of randomly sampled wells; one well in a separate, deliberately targeted group exceeded the public-water atrazine standard. Detection does not mean every result exceeded a health limit. The DNR lists atrazine among pesticides found in well analyses and notes that land application, handling, spills, well construction, and local geology can all affect whether pesticides reach groundwater. A 2023 peer-reviewed study of 47 northeast Iowa farm taps found mixtures of pesticide-related compounds, inorganics, and microbes. It was a focused sample of vulnerable settings, not a statewide prevalence estimate.
The PFAS question needs its own test
Biosolids are treated sewage solids used as fertilizer. Associated Press reporting describes how PFAS already present in wastewater can remain in biosolids; Iowa Environmental Council researchers identify land application as a potential route into soil and groundwater and call for PFAS testing of biosolids. The same report says Iowa does not require that monitoring. Iowa’s routine private-well tracker covers nitrate, bacteria, and arsenic, not PFAS. So the nitrate map cannot tell a household whether its well contains PFAS, much less prove where any PFAS came from. AP has documented wells affected by sludge-related PFAS in Wisconsin; that case demonstrates the pathway, not an Iowa-wide finding.
If your home uses a private well
The Iowa DNR recommends annual testing for nitrate and bacteria. Ask your county environmental health office about the state’s Grants to Counties program and whether your location or nearby land use calls for additional pesticide or PFAS testing. A county average cannot substitute for a test at your tap. If a result is above the nitrate drinking-water limit, follow the DNR’s guidance on safe water and treatment; water above 10 mg/L should never be given to infants under six months.
The cost of discovering a problem should not fall silently on the household at the end of the field. Better county testing and tighter controls on nitrogen loss, manure handling, and biosolids monitoring would put the evidence—and the responsibility—where it belongs.
