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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
Top 20 of 1,134 by populationChicago
IL0316000 · 2,746,388 served
Aurora
IL0894070 · 183,000 served
Joliet
IL1970450 · 160,000 served
Naperville
IL0434670 · 156,406 served
Il American-champaign
IL0195300 · 150,000 served
Rockford
IL2010300 · 147,051 served
Il American-peoria
IL1435030 · 137,575 served
Il American-east St Louis
IL1635040 · 131,368 served
Springfield
IL1671200 · 117,444 served
Elgin
IL0894380 · 114,797 served
Waukegan
IL0971900 · 87,149 served
Cicero
IL0310510 · 83,000 served
Aqua Illinois-kankakee
IL0915030 · 80,000 served
Bloomington
IL1130200 · 77,610 served
Decatur
IL1150150 · 76,122 served
Schaumburg
IL0314890 · 75,750 served
Evanston
IL0310810 · 74,486 served
Il American-west Suburban
IL1974151 · 73,978 served
Arlington Heights
IL0314030 · 73,320 served
Palatine
IL0312340 · 70,875 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