Oak Park Water Hardness & Quality Report (2026)

The Village of Oak Park Public Works Department supplies drinking water to approximately 52,000 residents across 4.7 square miles in Cook County, Illinois, purchasing fully treated water from the City of Chicago's Department of Water Management. The primary source is Lake Michigan, drawn through intake cribs in the lake and processed at major facilities including the Jardine Water Purification Plant and the South Water Purification Plant, both located along Chicago's lakefront. No local groundwater wells are reported in service.

The supply originates from the Lake Michigan watershed, shaped by Pleistocene glacial geology. Underlying Silurian-age Niagaran dolomite and limestone series interact with water during treatment and conveyance, imparting minerals. Shallow aquifer systems in the area — comprising Quaternary glacial till and outwash sands overlying carbonate bedrock — contribute to the moderately mineralised to hard character through natural calcium and magnesium dissolution, though the dominant lake source moderates extreme hardness.

At this hard level, water causes noticeable scale buildup in pipes, water heaters, dishwashers, and washing machines, reducing efficiency and lifespan. Faucet aerators and showerheads clog over time, contributing to higher energy bills and dry skin from soap scum residue. Regular annual descaling of appliances and installation of a water softener are recommended to protect plumbing and improve cleaning performance. Chicago's water maintains pH around 8–9 for corrosion control using orthophosphate inhibitors, and the supply complies with EPA lead and copper rules. No recent PFAS exceedances have been reported in Consumer Confidence Reports; treatment at the Chicago plants includes screening, chemical coagulation, filtration, and chlorination, with seasonal taste and odor management for algae.