It’s not usually open to the public, but the once-a-year Doors Open Toronto event invites everyone to take a peek inside a collection of heritage buildings and city infrastructure. The interwar water treatment plant still provides about a third of Toronto’s drinking water supply at nearly a billion liters a day. The National Historic building is also the largest Art Deco complex in the city.
The plant filters water from Lake Ontario and chlorinates it to control organism growth and get rid of large debris. Then, it’s pumped into mixing chambers to let aluminium sulphate to bind to impurities and settle to the bottom of the basin. The old building still uses lead pipes, so orthophosphate is added to form a thin layer of protection against corrosion. Anthracite and sand filters out microorganism and fine particles from the water and further chlorination disinfects the water. Excess chlorine is removed while fluoride is added to fight tooth decay.
The water flows by gravity to end users in 14 km of pipes via John Street and Parkdale pumping stations. The debris, organisms, and particles removed from the water by the plant are further filtered before being returned to Lake Ontario. Whatever residue is too thick sits at the bottom of decant tanks to be processed for landfill.
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