Rock Island County, Illinois: drinking water report. Rock Island County in northwestern Illinois has about 143,000 residents in the Quad Cities
Rock Island County in northwestern Illinois has about 143,000 residents in the Quad Cities metropolitan area, including Rock Island, Moline, and East Moline. Water comes from the Mississippi River, treated by Iowa American Water and Illinois American Water. Rock Island Arsenal – a 946-acre island in the Mississippi that is the U.S. Army's largest government-owned weapons manufacturing arsenal – sits in the heart of the county.
Rock Island Arsenal has confirmed PFAS contamination from AFFF firefighting foam. According to the Army's 2024 environmental investigation, monitoring wells on the island show PFOS at 42 ppt. The contamination has been detected in groundwater discharge to the Mississippi River, though the river's enormous volume dilutes the impact at downstream intakes.
The Mississippi River at the Quad Cities carries agricultural runoff from Iowa and Illinois. A 2024 USGS monitoring report documented atrazine at 1.9 ppb and nitrate at 5.4 mg/L during spring at the Quad Cities gauge. Treatment plants manage these levels, but the seasonal agricultural pulse drives disinfection byproduct formation.
The Quad Cities' Mississippi River supply is treated and meets all standards. The agricultural seasonal pattern means spring and early summer typically produce the highest contaminant concentrations in raw water. Rock Island Arsenal's PFAS is primarily a groundwater and on-island concern rather than a threat to the municipal supply.
Check your water for data at your address. A carbon filter addresses atrazine and seasonal taste changes. For PFAS, reverse osmosis provides additional protection. Our water filter guide covers systems suited to treated river water. Pull your detailed report for seasonal data, and visit our Illinois page for statewide patterns.