Whitchurch–Stouffville's water supply system is both groundwater-based with five municipal wells and since 2009 lake-based (Lake Ontario) as well. 5,500 cubic metres of water are withdrawn from the Oak Ridges Aquifer and the Thorncliffe Aquifer daily. Stouffville's well-water is chlorinated for disinfection, and sodium silicate is added to keep iron from staining plumbing fixtures and laundry. Two wells receive additional disinfection through an ultraviolet (UV) system. Three groundwater wells are in close proximity to the settlement area of Stouffville (Main Street, east of 10th Line); consequently 239 "significant drinking water threats" have been identified.