An independent study of five Cedar Valley cities found nitrate levels in drinking water can vary widely across neighborhoods, even in the same municipality.
Cedar Falls-based environmental scientist Kamyar Enshayan conducted the study between February and June this year, delivering samples from 41 taps located in homes and businesses in Waverly, Cedar Falls, Waterloo, Hudson and Cedar Rapids to the University of Iowa for analysis.
No samples exceeded 10 milligrams per liter (mg/L), the maximum level allowed by federal guidelines. However, the study does show that nitrate levels can vary widely by location, depending on municipal water sources and systems.
Enshayan, who retired as director of the University of Northern Iowa’s Center for Energy and Environmental Education in 2025 and formerly served on the Cedar Falls City Council, became curious about the role of location in determining nitrate consumption.
In communities like Cedar Falls, Waterloo and Waverly, source water comes from multiple wells rather than a centralized treatment plant.
“Some wells have high nitrate levels and others don't,” Enshayan said. “So, how do you know? What's your level of exposure? That was really what inspired doing these measurements.”
The study found wide disparities in some communities. Nitrate levels in Waverly varied from an average of 5.86 mg/L at a tap in the city’s center to an average of 9.66 mg/L at a tap to the south.
Disparities in Waterloo are even sharper. Multiple samples taken from taps north of the Cedar River were 10 to 15 times higher than taps to the river’s south.
“I was really surprised seeing communities that had very wide-ranging [levels] in what people are drinking," Enshayan said. "I would say that's a little discovery and just understanding of how things work."
Utility managers in Cedar Falls and Waterloo attributed the variations to differences in the surrounding geology, source water and depth of their wells.
Waterloo, for example, draws from 14 wells, five of which feed into a central reservoir. The remaining nine are located around the city’s periphery. Although city pipes are interconnected, Waterloo Water Works General Manager Chad Coon said water does “stay somewhat localized.”
As a result, neighborhoods located near higher-nitrate wells tend to have higher readings. Coon said the city is making efforts to phase out higher-nitrate wells and replace them with aquifers more isolated from nitrate pollution.
Nitrate pollution enters waterways from commercial fertilizers and farm animal waste, as well as non-agricultural sources, such as the natural decay of organic matter.
Centralized water works facilities reduce variability between neighborhoods. Cedar Rapids, for example, treats its water at two central plants. Averages from seven taps sampled in the study range from 6.78 mg/L to 7.37 mg/L.
While variability between locations is low, the study found fluctuation over time, as readings rose between February and June. According to Cedar Rapids' website, levels often rise during this period as “rain and snowmelt wash fertilizer residues from farm fields into the river.”
No samples exceeded the federal guideline of 10 mg/L, and consumer confidence reports from the utilities say its product is safe according “to state and federal drinking water standards.”
Enshayan contends that the federal guidance, which is based on a 1962 U.S. Public Health Service recommendation, is “outdated.” He pointed to more recent findings that link consistent exposure to nitrates above 5 mg/L to elevated cancer risk.
Enshayan hopes an increasing understanding of nitrate levels in drinking water will lead to community conversations.
“What are the level of risks? What can be done short term? What should be done long term? These are very important questions," he said. "But these discussions haven't happened at the community level."
He hopes those conversations will create policy change to address nitrate pollution “upstream.”
