September 6, 2004

Harmless compound gives earthy odour to Toronto water

TORONTO, ONT-An earthy odour in Toronto's water supply which became noticeable last week is being attributed to geosmin, a naturally-occurring compound present at extremely low levels (measured in parts per trillion) in Lake Ontario. The city's works and emergency services department notes that taste and odour episodes are caused by seasonal biological changes in the lake and typically occur in the late summer or early fall. Toronto's tap water continues to be safe to drink: geosmin is not harmful to public health and the city's water quality is not otherwise affected. These episodes normally dissipate after the lake water temperature starts to go down (below 15*C). Two of Toronto's four water filtration plants (Island and R.C. Harris) are permanently retrofitted with interim granular activated carbon systems which reduce geosmin, but do not eliminate it entirely. The other two water filtration plants (RL Clark in the west end and FJ Horgan in the east end) have powdered activated carbon systems, which must be activated at the time of a taste and odour episode. Once the carbon systems in these two plants are activated, it may take from a few hours to a few days for the filtered water to reach consumers' taps. Recommended strategies for reducing taste and odour in drinking water include keeping a jug of water in the refrigerator and adding ice cubes or a few drops of lemon juice.
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