Residents on Montreal's West Island are being warned to avoid using their water because of unusually low levels of chlorine.
The warning affects people in Baie D'urfé, Beaconsfield, Ste-Anne-de-Bellevue, southern parts of Senneville, southern parts of Dollard-des-Ormeaux, Kirkland and Pointe-Claire.
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Authorities say they found a problem at the Pointe-Claire water treatment plant on Friday during routine tests.
Low levels of chlorine were recorded, enough to potentially make someone sick.
People should avoid drinking their water, and using it for cooking or teeth-brushing.
Showers and baths are safe, as long as no water is swallowed.
The water is safe to use for washing dishes and clothes.
Authorities say boiling the water will make no difference because it is a problem caused by chlorine.
About 100,000 households in seven municipalities are affected.
Authorities say they hope to remedy the situation by Saturday.