Nitrate contamination has been a problem in Wisconsin for decades, and it's getting worse. Here's why.
MADISON - When Wisconsinites think about unsafe drinking water, their first thought might be the "forever chemicals" known as PFAS. Or it might be the thousands of lead pipes that communities, particularly Milwaukee, are being pushed to replace.
But the most widespread contaminant of Wisconsin's groundwater — the source of nearly 75% of the state's drinking water — is nitrate.
Nitrate contamination has been a problem in Wisconsin, and elsewhere, for decades. In a 2023 report to the Legislature, members of the state's groundwater coordinating council wrote that it is "increasing in extent and severity."
When public water systems experience elevated nitrate, the system has to take corrective action to keep consumers of that water safe. But with private wells, landowners — in most cases, the people who drink from the wells — are responsible for checking to see whether their water is safe. Of the data the state has on private wells, about one in 10 fail to meet the state's drinking water standard for nitrate — but more than a third of private well owners have never tested for the contaminant.
What is nitrate? Where does it come from, and how does it affect our health? Here's what to know.
What is nitrate?
Nitrate is a molecule that forms when ammonia or other nitrogen-rich sources, including nitrogen fertilizer, combine with oxygen. It dissolves easily into water, but does not absorb into the soil.
Generally, where pollution sources are absent, levels in groundwater are below 2 parts per million. Higher levels are seen where fertilizers are used in agriculture, or for grass or turf. Animal waste, septic systems or wastewater also could produce higher levels.
How does it end up in Wisconsin water?
Nitrate isn't soaked up by soil, so when too much is applied on agricultural fields, lawns or released some other way, it can percolate through the soil and into groundwater or run off with rainwater or snowmelt into lakes, rivers and streams.
Groundwater nitrate can make its way into drinking water through wells that pull up water for private homes or municipal water systems. Groundwater can run into surface water as well, meaning that nitrate in groundwater eventually ends up contaminating surface waters.
1994 research from the University of Wisconsin-Stevens Point found that 90% of nitrogen inputs to groundwater can be traced to agriculture, with the rest coming from septic systems and lawn fertilizer. Kevin Masarik, a groundwater education specialist at UW-Stevens Point, said the breakdown of sources has likely not changed since then.
How does nitrate affect human health and the environment?
Studies suggest that drinking water with elevated levels of nitrate over a sustained period can cause birth defects, thyroid problems and colon cancer. Pregnant women and babies are the most vulnerable. The contaminant has been associated with a condition called blue baby syndrome, which reduces the amount of oxygen in a baby’s blood.
Too much nitrogen in surface water can also harm the environment. It can create algae blooms, as does phosphorus. Those blooms have plagued some Wisconsin lakes and other bodies of water, closing beaches and making conditions unsuitable for recreation.
When those blooms die off, the algae sinks to the bottom and decomposes, sucking oxygen from the water. Perhaps the most infamous instance of this is the Dead Zone in the Gulf of Mexico, but places nearer to Wisconsin have dead zones, too, including the bay of Green Bay.
Which parts of Wisconsin deal with high nitrate levels?
Kewaunee County is typically held up as an area struggling with nitrates.
The county is perched upon karst geology, which consists of porous, cracked rock through which water easily travels. That means when fertilizer or manure is applied in large quantities, it can more easily make its way into the groundwater and impact the wells that draw from it. The county also has a high concentration of large farms, or concentrated animal feeding operations, which means that more manure is spread on agricultural fields.
But it's not alone, nor is it facing the worst contamination. The program director of the Wisconsin Department of Natural Resources' Bureau of Drinking Water and Groundwater, Steve Elmore, said portions of the state that have sandy soils and intensive agricultural areas tend to have the most problems with nitrate.
He pointed to more rural areas of Dane County, south central Wisconsin, the state's Central Sands region and a small pocket west of Eau Claire.
The DNR estimates about one in 10 private wells in Kewaunee County exceed the standard for nitrate in drinking water. In Portage and Dane counties, Elmore said, it's closer to one in five.
How does Wisconsin regulate nitrate?
In drinking water, Wisconsin sets its health-based standard for nitrate at 10 mg/L.
In 2019, the DNR attempted to set performance standards to regulate farmers' use of manure and fertilizer on soils susceptible to nitrate contamination. The agency scrapped its plan in 2021, saying the process and timeline set by the state's statutes did not allow adequate time for the rulemaking to move forward. No indications have yet been made that the DNR or state Legislature plans to pick up a new rule any time soon.
How can I have my water tested for nitrate?
People who get their water from private wells should have them tested at least annually for nitrate, the Wisconsin Department of Health Services recommends. The water should be tested before it will be consumed by infants or someone who is or could become pregnant, or if it changes color, taste or smell.
To learn more about testing your well water, visit dnr.wisconsin.gov/topic/Wells/privateWellTest.html or contact your local health department.
Laura Schulte can be reached at leschulte@jrn.com and on X at @SchulteLaura. Contact Madeline Heim at mheim@gannett.com.
This article originally appeared on Milwaukee Journal Sentinel: What to know about nitrate in Wisconsin waters, and the risk it poses
