How much Chlorine is too much?
Each day, the City of Toronto treats more than 1 billion litres of safe drinking water at four water treatment plants, which operate 24 hours a day, seven days a week.
How treatment works
- Water is collected from Lake Ontario through intake pipes deep below the lake and one to five kilometres away from shore.
- Lake water passes through screens to remove large debris and then through filters to remove additional impurities. Water is disinfected by using either chlorine or ozone.
- Alum or Poly Aluminum Chloride is added to the water to form a jelly-like substance that joins larger particles called floc, and goes through additional filtration.
- The water travels though settling basins so larger particles settle to the bottom. The clear water at the top proceeds to filters containing gravel, sand and carbon to remove suspended impurities and bacteria.
- Before water is pumped for distribution to homes and businesses, the following is added:
- chlorine to destroy bacteria, algae and viruses
- fluoride to help prevent tooth decay
- ammonia to ensure chlorine levels remain consistent as water travels through the distribution system
- phosphoric acid, which is used for corrosion control to help create a barrier between residential lead pipes and drinking water
Supply, storage and distribution
To ensure an uninterrupted water supply, there is a computerized process control system overseen by Toronto Water staff. The aim is to distribute superior quality water in a reliable, cost-effective and environmentally sound manner. Staff monitor:
- four water treatment plants
- almost two dozen pumping stations and filtration plants
- 11 underground reservoirs
- four elevated storage tanks
- more than 6,000 km of watermains
To ensure adequate water pressure and supply, Toronto is split into six pressure zones and subdivided into 13 pressure districts, which are continuously monitored and adjusted based on demand. Additional water is stored in tanks and reservoirs, which helps maintain pressure and enough supply during peak periods and emergencies such as fires, watermain breaks and power outages.
Drinking water system & financial reports
See the most recent reports submitted to the Ministry of the Environment, Conservation and Parks regarding the operations, capital and operating budgets of the drinking water system.