Residents of the small Canterbury settlement of Governors Bay have been advised to boil their water following the discovery of E. coli in the town's water supply.
"All water that is used for drinking, food preparation, utensil washing, brushing teeth or making ice should be boiled until further notice," said Christchurch City Council Head of Three Waters and Waste John Mackie.
"We will be chlorinating the water to kill the E. coli but it is going to take a couple of days to flush the network and to get confirmation the water supply is clear of contaminants so until that happens it is important people heed the boil water notice."
Mackie said it was possible the E. coli contamination was caused by the heavy rain over Easter weekend contaminating the Hayes 2 reservoir that supplies water to parts of Governors Bay, but that was yet to be confirmed.
Until the source of the contamination was confirmed, the council and Community Public Health were taking a precautionary approach and issuing a boil water notice to the whole of Governors Bay.
An estimated 350 properties are affected.
The presence of E. coli in the water supply was only confirmed by the laboratory this morning after water samples were taken yesterday.
"We've informed the Canterbury District Health Board of the discovery and are working with them to get the word out to homes, schools, businesses, childcare and healthcare facilities in the affected area," Mackie said.
The boil water notice would remain in place until laboratory tests confirmed the water was safe to drink.
Dr Ramon Pink, Canterbury Medical Officer of Health, said it was important residents in the Governors Bay area boiled or treated all tap water before drinking, brushing teeth or using it in food preparation.
"Bringing water to the boil is sufficient to kill bugs. If you cannot boil water, treat it by adding 1 teaspoon of household bleach per 10 litres of water and leave for 30 minutes," Pink said.
"The Christchurch City Council and Canterbury DHB's Community Public Health are working together to test water supplies in Governors Bay and will update this advice as soon as we have a clear idea of how the water supply has been impacted."
Pink said contaminated water could cause gastroenteritis.
"Gastroenteritis is usually self-limiting, and will settle within one to two days. Dehydration is the main concern and so drinking plenty of fluid is important. Most people will not need to see a doctor but if your symptoms persist, or you are concerned, call your GP team for advice."