Customers at 3,600 properties in a South Yorkshire village have been told not to use their tap water.
Yorkshire Water said "high levels of bacteria" had been detected in water supplying Thorne near Doncaster.
The firm has apologised and delivered bottled water to those affected.
Spokesman Charlie Haysom said: "We are working hard to identify the source of the contamination and carrying out widespread flushing and sampling in the area".
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