Illinois Tap Water Quality
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Overview
Northeastern Illinois drinks Lake Michigan water treated at Chicago's enormous filtration plants and piped to more than 100 suburbs; the lake supply is excellent and consistently compliant. Downstate cities rely on rivers and wells of varying character.
Illinois' defining issue is lead: the state has more lead service lines than any other, roughly 1 million, with Chicago alone holding about 400,000. Statute now requires full replacement over the coming decades. Radium in deep-aquifer groundwater has long affected some collar-county and downstate systems, and PFAS sampling has flagged sites near industry and bases.
Common Contaminants in Illinois
The nation's largest lead-line inventory; corrosion control keeps water compliant while a decades-long replacement mandate proceeds
Naturally occurring in the deep sandstone aquifer; several small systems treat or blend to comply
Agricultural runoff seasonally pressures river-sourced downstate systems like Decatur
Statewide sampling found detections near industrial corridors; Illinois has proposed enforceable limits
Violations & Compliance
Lake Michigan systems rarely violate standards. Downstate, radium and occasional nitrate exceedances in small systems make up most health-based violations, and lead-line replacement dominates the compliance agenda statewide.
Water Hardness in Illinois
Hard, typically 120–300 mg/L. Lake Michigan systems (Chicago and suburbs) sit around 120-140 mg/L, while downstate groundwater systems on glacial and limestone aquifers are very hard.
Hardness affects taste, limescale, and soap — not safety. Compare levels across all cities or read the water hardness guide.
City Water Reports in Illinois
Frequently Asked Questions
Sources & References
The safety rating and guidance on this page draw on the following sources. See our full methodology.
- •US EPA Safe Drinking Water Act regulations
- •EWG Tap Water Database
- •The utility's most recent Consumer Confidence Report (CCR)
- •WHO Guidelines for Drinking-water Quality