Water Quality

Tap Water Safety

Canadians have one of the largest fresh water supplies in the world. And here in Toronto, we're especially fortunate to live on the shores of the Great Lakes. Affordable, clean water flows from our taps. Our water supply is subject to 'on-line' testing, continual samplings and read outs, and daily testing for bacteriological quality. Drinking water analysis for hundreds of trace chemical compounds shows that most are not detectable and the few that are detected are well below Canadian and Ontario Drinking Water Guidelines. These tests, conducted by Toronto Water, confirm excellent water quality its water treatment plants and throughout the water distribution network.

Household treatment devices and bottled waters are not subject to the same government regulation as your municipal water supply. Devices and bottled water can be highly inconsistent in the water quality they provide. Improper usage or maintenance of a home treatment device can result in drinking water with harmful chemical or bacteria levels.

Chemicals are used to treat your water

Considering the many harmful substances and situations you can find yourself in every day, your drinking water should be the least of your worries! Yes, chemicals are used in the water treatment process. However, Toronto Water uses the lowest amount of chemicals necessary to treat the water effectively. Two chemicals which cause people concern are chlorine and aluminum. Here is information about the use of these chemicals in our water treatment process.

  1. Chlorine

    Chlorine is used to control bacteria, algae and viruses present in the water. Chlorine must be present at all times in the water, within the Ministry of the Environment and Climate Change regulatory requirements, to maintain the quality and safety of water as it leaves the treatment plants and travels through the distribution system.

    Some residents may be sensitive to chlorine taste and odours. In order to alleviate chlorine taste and odour concerns, residents can fill a pitcher with water and let it stand overnight in the refrigerator to help dissipate some of the chlorine. 

    Trihalomethanes (THM) are a group of chlorine by-products that form when water containing organic matter is chlorinated. In December 1995, Health Canada's Great Lakes Basin Cancer Risk Assessment Study released a report which linked long term use (over 35 years) of water containing elevated THM levels to an increased risk of bladder and colon cancer. THM levels that were above 50 parts per billion (ppb) were cited as a cause for concern. The average THM level in water produced at Toronto's water treatment plants during 2016 was 11 ppb, considerably below the level of concern.

  2. Aluminum

    Aluminum sulphate (alum) has an essential function in the water treatment process. It helps remove harmful micro-organisms and particles by making them clump together into larger particles so they can be filtered out of the water supply. Although most of the aluminum is removed during the treatment process, a small amount remains in the water.

    A research study published in the Canadian Journal on Aging reported a possible link between aluminum levels above 250 ppb in water and Alzheimer's Disease. Extensive research has been conducted, however medical researchers have not concluded that aluminum causes Alzheimer's Disease. Toronto Water closely monitors aluminum levels in drinking water from the filtration plants and levels are below the Ontario guideline levels. The average aluminum level in water produced at our water treatment plants during 2016 was 40 ppb.

Taste and odour concerns

Occasionally during the summer months, the presence of naturally-occurring algae and higher water temperatures in Lake Ontario can cause a noticeable taste and odour. Testing at quality control laboratories has confirmed that the quality of the water continues to be excellent during these occurrences. Toronto Water is looking at ways to reduce or eliminate the taste and odour episodes in the future.

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