The municipal water supply in Sundsvall, a town of 51,000 people, tested positive for coliform, a pathogen that itself is not harmful but whose presence indicates the possibility of other bacteria that could make people sick, TheLocal.se reported Saturday.
It's thought as many as 40,000 residents may have been exposed to the tainted water.
Town officials said the municipal water supply has been chlorinated to kill any potentially harmful bacteria but it might take as much as a day for the chlorinated water to reach all the homes in the area.
The cause of the contamination was under investigation.
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