Water in Kaiapoi has tested positively for the bacteria E.coli, prompting a reminder to people to boil their water for at least three minutes.
Many pipes in the Waimakariri region remain damaged after a 7.1-magnitude earthquake hit Canterbury on 4 September.
E.coli can cause stomach upsets. Its discovery in water is not unexpected given the severe damage, but health authorities say its ill-effects can be offset by boiling water continuously.
The boil water notice remains in place in Kaiapoi, Pines Beach and Kairaki.
Warning to avoid waterways
The contamination of sewage and wastewater has prompted a warning to people in Christchurch and Kaiapoi to avoid waterways.
The Canterbury Regional Council says the contamination is the result of quake damage to infrastructure and affects the Avon, Heathcote, Halswell and Styx rivers, as well as the estuary and tidal reaches of the Kaiapoi River.
The council says no one should drink water from any of these waterways, nor collect shellfish or fish, including whitebait.
It also urges people not to use rivers or the estuary for recreational activities such as boating and swimming.