Cook County, Illinois: drinking water report. Cook County encompasses Chicago and over 130 suburban municipalities, serving a combined population north of…
Cook County encompasses Chicago and over 130 suburban municipalities, serving a combined population north of 5.1 million. While the city's water comes from Lake Michigan via the Jardine and South treatment plants, suburban Cook County is split – some communities purchase Chicago water wholesale, while others operate independent treatment systems drawing from Lake Michigan or deep aquifer wells. This patchwork means two neighbors on opposite sides of a municipal boundary might drink entirely different water.
Lake Michigan provides a generally clean source, but the infrastructure between the treatment plant and your faucet introduces risk. Cook County contains an estimated 400,000 lead service lines, the largest concentration in the nation according to a 2022 Natural Resources Defense Council inventory. Lead enters water after it leaves the treatment plant, which is why citywide averages can mask household-level exposure.
On PFAS, the EPA's UCMR5 program has detected compounds at multiple sampling points across Cook County systems. Suburban systems drawing groundwater – particularly near O'Hare International Airport, where firefighting foam has been used extensively – show higher PFAS readings than Lake Michigan surface water intakes. Illinois has proposed but not yet finalized state-specific PFAS standards.
Start by identifying whether your water comes from Chicago's system, a suburban Lake Michigan intake, or a groundwater well. The answer shapes your risk profile entirely. Check your water with our ZIP code tool to see contaminant data mapped to your specific provider.
If you live in a pre-1986 home, lead is a real concern regardless of your water source. Run your tap for 2-3 minutes after periods of non-use, and consider a pitcher filter certified for lead reduction. For PFAS concerns near O'Hare or in western suburbs, our water filter guide covers which systems actually remove these compounds. Pull your detailed report for historical trends, and see our Illinois page for statewide context.