A boil water notice has been issued for parts of eastern Christchurch.
Traces of E.coli have been found in the water supply in parts of Shirley, Bexley, Wainoni and New Brighton.
The notice affects around 2000 homes.
The Christchurch City Council says all water used for drinking, food preparation, washing utensils and brushing teeth should be boiled first.
"The boil water notice will remain in place until laboratory tests confirm the water is safe to drink," said reticulation and maintenance manager Tim Drennan.
"Bringing water to the boil is sufficient to kill bugs. If you cannot boil water, treat it by adding one teaspoon of household bleach per 10 litres of water and leave for 30 minutes."
The cause of the contamination is not yet known.
"The boil water notice will remain in place until laboratory testing confirms the water is safe to drink."
A map of the affected area can be found on the council website and below.