Des Moines has a distinction no city wants: it operates the world’s largest nitrate removal plant. The facility on the city’s northwest side runs whenever the Raccoon River — one of Des Moines’ two primary drinking water sources — carries nitrate above the EPA’s safe limit of 10 milligrams per liter. In recent years, that’s been happening more often and for longer stretches.
The nitrate comes from corn and soybean fields across northwest Iowa. Synthetic nitrogen fertilizer, hog confinement operations, and tile drainage systems that funnel subsurface water directly into streams have turned Iowa’s rivers into one of the most nutrient-loaded water systems in North America.
The Raccoon River: America’s Most Nitrate-Laden Water Supply
The Raccoon River drains 3,600 square miles of some of the most intensively farmed land in the world. Row crops — primarily corn and soybeans — cover over 80% of the watershed. The nitrogen applied to those fields doesn’t stay put. Rainfall dissolves it and moves it through the soil into tile drains that empty directly into creeks and rivers with virtually no natural filtration.
USGS monitoring has consistently ranked the Raccoon River among the most nitrate-contaminated rivers in the country. Annual average concentrations regularly exceed 10 mg/L — the point at which Des Moines Water Works must activate its nitrate removal system to meet Safe Drinking Water Act standards. During wet springs when planting-season fertilizer application coincides with heavy rainfall, the river can spike to 20 mg/L or higher.
The health concern is real. Nitrate at elevated levels interferes with blood’s ability to carry oxygen — a condition called methemoglobinemia, or “blue baby syndrome,” that can be fatal to infants. The EPA’s MCL was set specifically to protect infants and pregnant women.
Des Moines Water Works also draws from the Des Moines River, which — while slightly less contaminated than the Raccoon — faces the same agricultural runoff dynamics. The blending of both sources allows some management of nitrate levels, but both rivers peak simultaneously during the same weather events.
The $4.5 Million Machine
The Des Moines nitrate removal facility uses ion exchange — passing water through resin beads that capture nitrate ions and release chloride in their place. The system can process up to 33 million gallons per day. When it runs, it costs roughly $4.5 million per year in chemicals, energy, and maintenance.
That $4.5 million is paid by Des Moines Water Works customers — city residents and businesses — not by the agricultural operations that created the problem. This cost transfer has been the source of enormous political tension in Iowa.
In 2015, Des Moines Water Works filed a federal lawsuit against drainage districts in three northwest Iowa counties, arguing that tile drainage systems should be regulated as point-source pollution dischargers under the Clean Water Act. The lawsuit was dismissed in 2017 on jurisdictional grounds, but it ignited a national debate about agricultural water pollution accountability that continues today.
Atrazine and Agricultural Chemicals
Nitrate isn’t the only farm-related contaminant in Des Moines’ source water. Atrazine — one of the most widely used herbicides in corn production — is applied across the Raccoon and Des Moines River watersheds every spring and has been detected in both rivers and in the city’s treated drinking water.
Atrazine is regulated under the Safe Drinking Water Act with an MCL of 3 micrograms per liter. Des Moines Water Works has generally kept finished water below that level, but atrazine is a potential endocrine disruptor at levels below the MCL. The EPA’s scientific review of atrazine has been ongoing for years amid intense lobbying by the agricultural chemical industry.
Herbicide runoff from Iowa fields peaks in May and June, precisely when spring rains are heaviest and river flows are highest. The timing creates a compounded treatment challenge: maximum nitrate, maximum atrazine, maximum flow — all at once.
Cryptosporidium and Pathogens
In 1993, Milwaukee’s drinking water supply was hit by a Cryptosporidium outbreak that sickened 403,000 people — the largest waterborne disease outbreak in US history. The pathogen came from the Milwaukee River, contaminated with cattle feces from upstream farms.
Des Moines faces a structurally similar risk. The Raccoon and Des Moines Rivers receive runoff from livestock operations, feedlots, and hog confinements throughout their watersheds. Cryptosporidium and Giardia are resistant to chlorine and require filtration for removal.
Des Moines Water Works uses enhanced treatment including filtration and UV disinfection to address pathogen risk. The Hazmat-style operational complexity of managing both chemical and microbial contamination from agricultural sources makes Des Moines’ water treatment among the most technically demanding in the Midwest.
Lead in the Distribution System
Des Moines has lead service lines in older parts of the city, concentrated in neighborhoods developed before the 1950s. The city has been working through its inventory and replacement program, prioritizing schools and homes with young children.
Des Moines Water Works adds orthophosphate for corrosion control and has tested below federal lead action levels. But the combination of aging infrastructure and water chemistry changes that can temporarily disrupt corrosion control means vigilance is warranted for residents in older homes.
What Des Moines Residents Can Do
The city’s treatment system is sophisticated and the finished water meets all standards — the nitrate removal plant exists precisely to ensure that. But the agricultural contamination pressures on the source water are increasing:
- Review the annual CCR — Des Moines Water Works publishes detailed water quality reports with every tested contaminant.
- Test for lead if you’re in an older home — free testing is available through the utility.
- Run the tap before drinking if you have lead plumbing.
- Support agricultural conservation — voluntary nutrient management on Iowa farms is the only long-term solution to the nitrate crisis; organizations like the Iowa Nutrient Reduction Exchange work on this.
- Filter for atrazine — activated carbon filters reduce atrazine levels for additional peace of mind.
If you’re concerned about your water quality, a certified water treatment professional can help you test your water and recommend the right solution for your home.