Toronto’s tap water comes from Lake Ontario and is treated at four City-run plants that together treat more than one billion litres a day, according to the City of Toronto. The City adds chlorine (and ozone at one plant) to disinfect the water and has added fluoride since 1963, at a level regulated under Ontario’s Safe Drinking Water Act.
Old web posts asked whether Toronto’s water contains fluoride, whether it uses chlorine or chloramine, and whether supply could “run dry”. The City’s published documents answer the first two directly and describe the size of the system, which is the context for the third. This page uses only those documents: the City’s tap water pages, its 2024 Drinking Water System annual report, and a 2011 Medical Officer of Health report on fluoridation.
Where the water comes from
The City states that Toronto’s drinking water comes from Lake Ontario, drawn through intake pipes between one and five kilometres from shore, deep below the surface. Details of the lake itself, including its depth and drainage, are in Lake Ontario and the rivers of Toronto. The 2024 annual report, filed under Ontario Regulation 170/03, describes the drinking water system as 4 water treatment plants, 18 pumping stations, 11 major underground storage reservoirs, 4 elevated storage tanks, about 540 kilometres of trunk watermains, and 5,570 kilometres of distribution watermains.
The four treatment plants
The City’s “fast facts” page and the annual report give these details. Capacity is the rated capacity stated by the City, and the share is the approximate share of Toronto’s drinking water the City attributes to each plant.
| Plant | Opened | Rated capacity | Approximate share | Notes from the City |
|---|---|---|---|---|
| R.C. Harris | 1941 (built in the 1930s) | 950 million litres a day | 30 percent | Named after R.C. Harris, Commissioner of Works from 1912 until his death in 1945; nicknamed “The Palace of Purification”; a national historic civil engineering site; 2701 Queen Street East |
| R.L. Clark | November 22, 1968 | 615 million litres a day | 30 percent | South Etobicoke; originally called the Westerly Plant |
| F.J. Horgan | 1979, expanded 2009 | 800 million litres a day | 20 percent | The City calls it the first and only plant using ozone as the primary disinfectant |
| Island | 1977 (current plant) | 440 million litres a day | 20 percent | On Centre Island, on the site of the City’s first treatment plant from the 1900s; its cold water also supports Enwave’s downtown cooling system |
The Island plant’s capacity appears as 440 million litres a day in the City’s current pages. A reader comparing older City reports may find a different number, so the page date matters.
Chlorine, ozone, ammonia and the question of chloramine
According to the City, lake water is disinfected with chlorine or ozone early in treatment. Before it reaches homes and businesses, chlorine is added to destroy bacteria and viruses. The City’s page says ammonia is added to maintain chlorine levels as water moves through the distribution system. The 2024 annual report lists the treatment chemicals used as alum, chlorine, sodium bisulphite, hydrofluosilicic acid, aqueous ammonia, and phosphoric acid.
The word “chloramine” does not appear on the City page. Chlorine combined with ammonia is the usual way chloramine is produced, but the City’s own wording describes the ammonia only as a way to maintain chlorine levels, and this article keeps to that wording. Readers with a specific concern, such as a fish tank or dialysis equipment, should ask Toronto Water directly.
Fluoride in Toronto’s water
A March 21, 2011 staff report from the Medical Officer of Health to the Toronto Board of Health states that Toronto’s drinking water has been fluoridated since 1963. The report records these changes in the fluoride level: 1.2 mg/L until 1999, 0.8 mg/L from 1999, and 0.6 mg/L from 2005. It gives Health Canada’s maximum acceptable concentration as 1.5 mg/L, the same figure as in Ontario’s drinking water quality standards, and notes that in 2007 a Health Canada expert panel recommended 0.7 mg/L as the optimal target. The report recommended that the Board of Health reaffirm its position to continue fluoridation, and it lists more than 100 national and international organizations that support the practice.
The City states that fluoride is added to help prevent tooth decay and that its levels are regulated under the Safe Drinking Water Act, administered by the Ontario Ministry of the Environment, Conservation and Parks. The 2024 annual report records fluoride results for the plants that fluoridate. The 2011 report says that fluoridating a municipal supply is a decision made by local municipalities with the provincial authority. The dental and medical evidence is summarized in the 2011 report for readers who want the City’s full reasoning.
Testing and reporting
- Samples from the treatment plants are tested for bacteriological quality every six hours, almost 6,000 times a year.
- More than 20,000 tests are done at the treatment plants each year.
- More than 15,000 tests are done on samples from the distribution system each year.
- The annual report lists adverse results reported to the Ministry, with the corrective action taken. For 2024 it records, for example, an incident on February 16, 2024, when a disinfection calculation fell below 1 for 38 minutes at one plant because of abnormally high ammonia in the source water. The plant was removed from service, and the report notes that updated calculations showed the ratio never dropped below 1.0 and that the ministry inspection noted no non-conformance.
Unlike the topic of “water crisis” in older posts, none of these documents describes a shortage. They describe a system with a combined rated capacity of 2,805 million litres a day (the sum of the four plant figures above) drawing on a lake of about 1,640 cubic kilometres. For how the system relates to utilities billing and services, see Toronto utilities: water, hydro, and city services.
Frequently asked questions
Is there fluoride in Toronto’s tap water?
Yes. The City states that fluoride is added to help prevent tooth decay, and a 2011 Medical Officer of Health report says Toronto’s water has been fluoridated since 1963. The level was lowered to 0.6 mg/L in 2005.
Does Toronto use chlorine or chloramine?
The City says it disinfects with chlorine or ozone and adds chlorine before distribution, with ammonia added to maintain chlorine levels. It does not use the word chloramine on its tap water page.
Where does Toronto’s drinking water come from?
Lake Ontario, through intake pipes one to five kilometres offshore, according to the City of Toronto.
How often is Toronto’s water tested?
Plant samples are tested for bacteriological quality every six hours, and the City reports more than 20,000 plant tests and more than 15,000 distribution tests each year.
Last verified: October 2026
Sources
- City of Toronto, “Tap Water in Toronto”: toronto.ca
- City of Toronto, “Fast Facts about the City’s Water Treatment Plants”: toronto.ca
- City of Toronto, Toronto Drinking Water System Annual Report 2024: toronto.ca (PDF)
- Medical Officer of Health, Water Fluoridation in Toronto, staff report to the Toronto Board of Health, March 21, 2011: toronto.ca (PDF)
- U.S. Environmental Protection Agency, “Physical Features of the Great Lakes” (lake volume): epa.gov archive
Related reading
- Lake Ontario and the rivers of Toronto
- Toronto Hydro: history of the utility
- Toronto Harbour and waterfront: history
- Toronto rainfall and storms: climate records
- Living in Toronto: city services, universities and the economy
Cite this page
APA: History of Toronto. (2026, October 25). Toronto Tap Water: Source, Treatment and Fluoride. http://localhost:8210/blog/toronto-drinking-water-fluoride-and-treatment
MLA: “Toronto Tap Water: Source, Treatment and Fluoride.” History of Toronto, 25 Oct. 2026, http://localhost:8210/blog/toronto-drinking-water-fluoride-and-treatment. Accessed .
Chicago: History of Toronto. “Toronto Tap Water: Source, Treatment and Fluoride.” Last modified October 25, 2026. http://localhost:8210/blog/toronto-drinking-water-fluoride-and-treatment.
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