The Selwyn District Council has issued the boil water notice after test results showed E.coli levels were above the recommended levels.
It is likely to be in place for several days.
The Ministry of Health advises people should boil or treat all water from their taps before drinking, brushing teeth or using it in food preparation.
Water used to make ice should also be boiled before freezing.
Bringing water to the boil will kill all the bugs but all tap water needs to be boiled even if the smell or taste of chlorine is present.
If you cannot boil your water, it can be treated by adding a teaspoon of household bleach per 10 litres of water and leaving it for 30 minutes
Employers should also make sure their staff are only consuming boiled or bottled water at work.
Residents should continue to boil water until the boil water notice is lifted.
Anyone who shows any symptoms of sickness should visit their doctor as soon as possible.
Updates about the boil water notice will be available here.
