A boil water warning has been given in Governors Bay, following the discovery of E coli in the Banks Peninsula township's water supply today.
The Christchurch City Council said it was possible heavy rain in the area, near the head of Lyttelton Harbour, over Easter weekend caused the contamination of a reservoir that supplied water to about 350 properties in the area - but this was yet to be confirmed.
Council spokesperson John Mackie said the presence of E coli in the water supply was confirmed by the laboratory this morning, after samples were taken yesterday.
Mr Mackie said it would be chlorinating the water to kill the E coli, but this would take a couple of days.
The Canterbury District Health Board said it had not had any notifications of people being sick as a result of the contamination.