Residents in the Hurunui township of Waiau are being advised to boil all water, after E.Coli was detected in its water system.
The Hurunui District Council said on Monday that the boil water notice is precautionary and temporary.
Drinking contaminated water has the potential to cause illness, including vomiting and diarrhoea.
The council says staff are dosing continuously with chlorine, but the treated water will still need to be boiled until further notice.
The water will be monitored until three consecutive clear test results are recorded.