St. Catharines draws municipal drinking water from Lake Erie (via Welland Canal intake near Allanburg), treated at Decew Falls Water Treatment Plant.
Ask where St. Catharines drinking water begins and the answer is Lake Erie (via Welland Canal intake near Allanburg), then Decew Falls Water Treatment Plant. That supply chain is what the water atlas puts beside hardness and lead.
Niagara Region conventional plant at 2700 Decew Road, St. Catharines. Three treatment trains; combined rated capacity 227,300 m³/day. Screening, coagulation/flocculation/sedimentation, filtration, sodium hypochlorite disinfection with UV enhancement. Canal water reaches the plant by a gravity supply channel about 5.4 km long.
See the St. Catharines water page for the grade, source notes, and municipal report links.