Grey District Council says due to recent bad weather, the council has not been able to replenish its raw water storage, which is now very low.
It says it may need to take water from the intake at Blackball Creek, which is lower quality - so all drinking water should be boiled until further notice.
People should conserve water where possible.
The council will start testing the water supply daily.
Grey District Council says it will provide any updates to the situation via their website and Facebook pages.