A boil-water notice is in place for West Melton, in Canterbury, due to high levels of E coli found in the town's water supply.
A Selwyn District Council spokesperson said a recent survey of the town's water supply found E coli levels were above recommended levels, probably because of recent heavy rain.
The water supply serves about 1800 people.
Water should be boiled until further notice, and if any resident felt sick they should contact their doctor, the spokesperson said.
Residents should expect to boil water for several days.