The Illinois River flows through the heart of the American Corn Belt. By the time it reaches Peoria, it has collected drainage from roughly 29,000 square miles of agricultural land in Illinois and Indiana, carrying with it the fertilizers, herbicides, and sediment that characterize intensive row crop farming. It’s also received discharges from cities and industrial facilities along its length. Peoria draws its drinking water from this river — and that means the city’s water utility is constantly managing a challenging source.
The Illinois River: A Stressed Waterway
The Illinois River has been described by state and federal environmental agencies as one of the most nutrient-impaired rivers in the United States. Nitrates from agricultural runoff are chronically elevated, particularly in spring when tile drainage carries dissolved nitrogen from cornfields into tributaries and then into the main stem. Phosphorus from fertilizer and livestock operations fuels algal growth.
The river has also been subject to industrial discharges over the years. Caterpillar, one of Peoria’s largest employers, has historically had large manufacturing operations in the region. Various industrial facilities along the river have held NPDES permits for discharges. The EPA’s Toxics Release Inventory documents the chemical releases from Peoria-area facilities.
Combined sewer overflows are another factor. Peoria’s sewer system, like those of many older Midwest cities, includes combined sewers that carry both stormwater and sanitary sewage in the same pipes. During heavy rain, when the system’s capacity is exceeded, CSOs discharge partially treated or untreated sewage into the Illinois River. The Peoria Sanitary District has been working under a consent decree with the Illinois EPA to reduce CSO frequency and volume through long-term control plan implementation. CSOs contribute bacteria, nutrients, and other pollutants to the river during and after storm events.
Peoria’s Drinking Water Source and Treatment
Peoria Public Works draws water from the Illinois River at an intake in the Peoria Pool, a reservoir formed by a lock and dam on the river. The raw water is treated at the Peoria Pumping Station and Water Treatment Plant, which uses conventional treatment processes: coagulation and flocculation, sedimentation, filtration, and disinfection with chlorine.
The challenge with Illinois River water is its variable quality. Spring snowmelt and rainfall drive surges in turbidity, nitrates, atrazine (a commonly used corn herbicide), and other contaminants from agricultural fields. The treatment plant has to manage this variability. Peoria has invested in additional treatment capacity and monitoring over the years, but it’s working with a source that throws it regular curveballs.
What the Data Shows
Peoria’s Consumer Confidence Reports provide the annual accounting of what’s detected and at what levels. Key contaminants of note:
Nitrates: The EPA MCL for nitrates is 10 mg/L. Illinois River nitrates can spike significantly above this level during spring runoff, particularly in March through May. Water utilities with river intakes have to manage these spikes through treatment or by temporarily switching to alternative sources if available. Monitoring the CCR for nitrate levels and whether they ever approach the MCL is important. [NEEDS VERIFICATION: specific nitrate spike events in Peoria water supply]
Atrazine: Atrazine is the most widely used herbicide in corn production, and the Illinois River carries significant atrazine loads during the growing season. The EPA MCL for atrazine is 3 micrograms per liter. Studies of Illinois River water have documented atrazine at or above this level during peak runoff periods. Peoria’s treatment plant monitors atrazine and has compliance with the MCL, but atrazine is routinely detected. The Environmental Working Group has flagged the presence of atrazine in Peoria’s water as a concern at concentrations below the legal limit but above EWG’s more conservative health thresholds.
Disinfection Byproducts: High organic matter in Illinois River water, particularly during spring runoff, leads to elevated formation of TTHMs and HAAs during chlorination. Peoria’s system has generally maintained compliance with EPA’s DBP rules, but this is worth watching in the CCR data.
Manganese and Iron: These naturally occurring metals are present in the Illinois River and can cause taste, odor, and aesthetic issues in tap water. They’re not health threats at typical levels but can indicate treatment challenges.
Agricultural Chemical Load
Atrazine is the most prominent agricultural chemical in the Illinois River, but it’s not the only one. The Illinois River watershed grows enormous quantities of corn and soybeans, and a suite of pesticides and herbicides are applied each season. Research by the Illinois State Water Survey and USGS has documented acetochlor, metolachlor, and other herbicides in Illinois River water. Most are at low concentrations and below regulatory limits, but they represent a mixture that receives relatively limited toxicological study as a combined exposure.
The Illinois EPA’s Ambient Water Quality Monitoring Network provides ongoing data on Illinois River water quality at multiple locations. This data is publicly available and allows residents and researchers to track trends over time.
What Residents Can Do
- Read the CCR carefully. Look specifically at nitrate, atrazine, TTHM, and HAA sections. Compare detected levels to EPA MCLs and note whether levels are trending up or down over years.
- Pay attention to spring advisories. Spring is the highest-risk season for agricultural chemical spikes in Illinois River communities. Some utilities issue precautionary advisories during extreme runoff events — know how you’d hear about one if it happened.
- Filter for atrazine and DBPs. Activated carbon filtration at the point of use is effective at reducing atrazine and disinfection byproducts. This is a practical step for households that want additional protection during high-risk periods.
- Private well users test independently. If you’re on a private well in the Illinois River watershed, test for nitrates, atrazine, and other agricultural chemicals annually. Agricultural chemical contamination of shallow wells in corn-farming regions is well-documented.
- Support agricultural conservation. Long-term improvement in Illinois River water quality depends on reducing nutrient and pesticide loads from the watershed. Conservation tillage, cover crops, and buffer strips along waterways are practices that help.
Water Treatment Options
For atrazine removal: granular activated carbon (GAC) and reverse osmosis are both effective. NSF/ANSI 53-certified carbon block filters at the point of use provide good atrazine reduction.
For nitrates: activated carbon does NOT remove nitrates. Reverse osmosis or ion exchange (deionization) are the effective options for nitrate reduction.
For disinfection byproducts: activated carbon filtration is effective for TTHMs and HAAs.
A combined approach — reverse osmosis with a carbon pre-filter — addresses all three of these concerns and is practical for under-sink installation in a kitchen.
The Illinois River’s water quality is fundamentally tied to how land is farmed in its vast watershed. Improving it requires policy, incentive programs, and time — not just better treatment plants. Until that progress materializes more fully, Peoria residents benefit from understanding what’s in their water and how to address concerns at home.
If you are concerned about your water quality, a certified water treatment professional can test your water and advise on solutions.