Peoria Water Hardness & Quality Report (2026)

Peoria, Illinois — the largest city on the Illinois River — draws its municipal water supply from the Illinois River via the City of Peoria Water Department, drawing from Lake Peoria — a natural broadening of the Illinois River in Peoria and Tazewell Counties — at the Robert E. Guth Treatment Facility. The Illinois River at Peoria represents a major confluence of Central Illinois drainage, collecting runoff from the upper Illinois basin, the Chicago metropolitan drainage system (including Lake Michigan diversion), and numerous large tributaries. Water hardness measures 183 mg/L — classified as hard.

Peoria's hard supply reflects the mixed carbonate geology of the Illinois River watershed. The Illinois River drains terrain underlain by: Mississippian Salem Formation, Ste. Genevieve Limestone, and Warsaw Formation (prolific carbonate formations of the Central Illinois Interior Platform); Pennsylvanian Carbondale Formation (coal measures with calcareous shale); and Quaternary Pleistocene glacial till and outwash derived from pulverised Paleozoic carbonate bedrock across the Illinois interior. Additionally, the Illinois River system at Peoria receives significant urban and agricultural runoff from central Illinois farmland, which contributes mineral loading from calcareous agricultural soils. The result is consistently hard water throughout the Illinois River corridor.

At 183 mg/L, Peoria residents face regular hard water challenges. Scale deposits form on faucet aerators, showerheads, and inside appliances within weeks — monthly descaling with citric acid solution is standard maintenance. Dishwashers produce better glassware results with rinse-aid, and water heaters benefit from annual inspection for element scale accumulation. City of Peoria Water Department consistently delivers water meeting all Illinois EPA and federal Safe Drinking Water Act requirements.