Hot weather can mean taste and odour problems for water
During the late summer or early fall, Toronto residents may experience a noticeable smell and musty tasting water. This is caused by seasonal biological changes in Lake Ontario, which produces a naturally occurring, odour-causing chemical compound, called geosmin. Even at very low levels, geosmin can be detected by some people.

The unpleasant taste and odour may make you think that the water is "off" and not safe to drink. Be assured that during periodic taste and odour events, your water is safe. Seasonal taste and odour in drinking water is not a threat to public health.

The City of Toronto is making every effort to reduce the impact of taste and odour events. Toronto's four water filtration plants were retrofitted with either powdered activated carbon or granular activated carbon systems. These systems reduce the effects of the smell and musty taste but may not eliminate it entirely.

If you should notice a taste and odour in your water during the summer or fall seasons, simple home remedies, such as keeping a jug of water in the fridge and adding ice cubes or some lemon juice to tap water should improve it. If you're experiencing taste and odour problems in your area, please let us know. Call the Water Quality Line at 416-392-2894.

Send your email to: askwater@toronto.ca

What if my water tastes or smells funny?
In the late summer or early fall, you may notice an earthy, musty smell and taste in your tap water. Natural, seasonal changes in Lake Ontario can cause this to happen. We're not alone; all cities and towns that draw their water from Lake Ontario suffer the same problems. Lake water temperatures, which over the year average six to seven degrees Celsius at the intake pipes, can climb to as high as 25 degrees. These high temperatures result in increased numbers of algae. Certain types of algae produce compounds that can result in a noticeable odour or taste even at extremely low levels. One of these is geosmin which is usually measured in parts per trillion (one million millions). Humans can detect its presence in concentrations as small as 10 parts per trillion. These episodes can result in concentrations of more than 50 parts per trillion, a level at which the compound can be easily detected by most people in their tap water.

Is this water still safe to drink?
Yes, your water remains perfectly safe to drink. The only change is the presence of these taste and odour-causing compounds, at trace levels, which are not harmful to health. Toronto's treated water supply is tested every four hours to confirm the absence of harmful bacteria. Extensive testing by Toronto's water laboratories during these "taste and odour" episodes confirm that the quality of the water continues to be excellent.

Can the taste and smell be reduced?
To make the water taste better, try chilling it, adding ice cubes or squirting in a few drops of lemon juice.

How long does the taste and smell last?
The duration of past episodes have ranged from a few days to 11 days. It is impossible to predict, at the onset of an episode, how long it will last. Generally, as the lake water temperatures drop, the problem begins to disappear.

Why doesn't the water treatment process remove the problem?
Water treatment plants can make operational changes to reduce the taste and odour effects to some extent when they occur. While algae is specifically removed during the water treatment process, compounds such as geosmin are not easily eliminated.

Is bottled water or water that comes from a home treatment device "better"?
Toronto's 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 confirm excellent water quality at Toronto's treatment plants and throughout the water system. 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 inconsistent in the water quality they provide. Improper use or maintenance of a home treatment device can result in drinking water with harmful chemical or bacteria levels.

How can Lake Ontario water be safe for drinking but not for swimming?
Because the "water" in question comes from different places and goes through different systems. Normally, sewage flows to Toronto's wastewater treatment plants for treatment before being discharged into the lake. During heavy rainstorms, however, rainwater and some sewage may overflow the sewer system and flow directly into the lake near the shore. Water from local Lake Ontario beaches is regularly tested by the Board of Public Health for bacteria contamination. When the bacteria levels are too high at particular locations, swimming may be unsafe so the beaches must be closed.

Drinking water, on the other hand, is drawn from Lake Ontario through special intake pipes that extend two to three kilometres into the lake and are 15 metres below the surface. These intakes are far from sources of local pollution. The water then passes through a water treatment plant where it undergoes an extensive treatment process. Even though the "water" comes from the same source, you can be very confident that your drinking water is safe to drink.

For more information on the water treatment process, please see our factsheet: The Drinking Water Treatment Process.