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Illinois Water Quality
1,134
Utilities in database
12.0M
Residents served
20%
On private wells
3
Key contaminants tracked
Drinking Water in Illinois
Illinois has 1,134 community water systems serving approximately 12.0 million residents. Primary water sources include groundwater. The most commonly reported contaminants include lead, disinfection byproducts, nitrates. 20% of Illinois residents rely on private wells. IEPA holds primary enforcement authority under the Safe Drinking Water Act.
Utilities in Illinois
226–250 of 1,134Waterloo
IL1330300 · 10,190 served
Maryville
IL1190750 · 10,150 served
Leyden Twsp Water District
IL0315880 · 10,000 served
Sauk
IL0312790 · 9,921 served
Winfield
IL0431150 · 9,835 served
La Salle
IL0990300 · 9,700 served
Steger
IL0314860 · 9,700 served
Clark-edgar Rwd
IL0230010 · 9,657 served
Itasca
IL0430500 · 9,506 served
Harvard
IL1110250 · 9,469 served
Rochelle
IL1410500 · 9,446 served
Oak Brook
IL0430700 · 9,400 served
Flossmoor
IL0310870 · 9,371 served
Riverside
IL0312670 · 9,298 served
Lynwood
IL0311680 · 9,149 served
Paris
IL0450300 · 9,100 served
Harwood Heights
IL0311140 · 9,065 served
Willowbrook
IL0431100 · 9,000 served
Glenwood
IL0311050 · 8,956 served
Monmouth
IL1870150 · 8,902 served
Clear Water Service Corp
IL0295100 · 8,900 served
Olney
IL1590200 · 8,877 served
Glencoe
IL0310990 · 8,849 served
Lake Villa
IL0970840 · 8,829 served
Mascoutah
IL1630800 · 8,759 served
Key Contaminant Concerns in Illinois
Lead
Lead is a naturally occurring heavy metal that was widely used in plumbing infrastructure until it was banned for new installations in 1986. An estimated 9.2 million lead service lines still connect homes to public water mains across the United States, along with millions of homes with lead solder in their internal plumbing.
Nitrates
Nitrate (NO₃⁻) is a nitrogen-containing compound that forms naturally through the decomposition of organic matter. At elevated concentrations — almost always from human activity — nitrate interferes with the blood's ability to carry oxygen. The United States produces over 23 million tons of nitrogen fertilizer annually, making agricultural runoff the dominant source of nitrate contamination.
DBPs
When utilities add chlorine to water to kill pathogens, it reacts with dissolved organic matter — leaves, algae, soil — to produce disinfection byproducts (DBPs). Over 600 DBPs have been identified. The EPA regulates two groups: total trihalomethanes (TTHMs, including chloroform) and haloacetic acids (HAA5). DBP levels tend to be highest in surface water systems and in warm months when organic matter is elevated.
Illinois Water FAQs
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Data source: Utility data from EPA SDWIS. 1,134 active community water systems ingested. CCR contaminant data ingestion in progress.
Last updated: 2026-04-17