The Selwyn District Council has launched an investigation into how its water supply became contaminated with E.coli, leaving dozens of residents ill.
The council says a water systems failure probably led to a spate of gastroenteritis in the town of Darfield in Canterbury last week.
Chief executive Paul Davey says last Thursday unacceptable levels of E.coli were recorded in the town's Waimakariri River water supply and a boil water notice was issued until three days of clear sampling were obtained.
Mr Davey says despite many levels of communication, he understands some residents did not hear about the notice in a timely fashion and the council apologises to anyone who became ill.
