Residents on the Arthur's Pass supply are being advised to begin boiling water following heavy rain in the region over the past few days.
A Selwyn District Council spokesperson says no E Coli has been detected in the water supply, but increased turbidity means treatment may not be effective.
The spokesperson says the council cannot guarantee the water is safe to drink and has issued a boil water notice as a precaution.
Residents should continue to boil their water until they are notified that the boil water notice is lifted. It is likely to be in place for several days.
Anyone who shows symptoms of sickness should visit their doctor as soon as they are able to.
The council will continue to monitor the intake and reticulation system and keep residents informed of any updates.
