St Clair County, Illinois: drinking water report. St. Clair County sits across the Mississippi River from St.
St. Clair County sits across the Mississippi River from St. Louis, with a population of about 260,000 including East St. Louis, Belleville, and O'Fallon. Water sources range from Mississippi River intakes to groundwater from the American Bottoms – the floodplain aquifer along the river. Scott Air Force Base, headquarters of U.S. Transportation Command, operates in the county's eastern section.
The American Bottoms aquifer beneath the county's western portion has been contaminated by decades of industrial activity. Zinc smelting, chemical manufacturing, and petroleum refining operations in the East St. Louis area left heavy metals and organic compounds in the shallow groundwater. According to the Illinois EPA's 2024 remediation report, seven active cleanup sites in St. Clair County involve groundwater contamination from industrial sources.
Scott AFB has confirmed PFAS contamination from AFFF firefighting foam. The EPA's UCMR5 data shows PFAS detections in water systems across the county. A 2024 IEPA assessment documented PFAS at concentrations above 10 ppt in three public water systems, including ones near the base.
Water quality in St. Clair County splits sharply between the eastern communities on cleaner aquifer water and the western communities near the industrial American Bottoms. Your location determines your risk profile.
Check your water for data specific to your system. For PFAS and industrial contaminants, reverse osmosis provides the broadest protection. Our water filter guide covers systems for multi-contaminant environments. Pull your detailed report for historical data, and visit our Illinois page for statewide context.