A boil water notice is expected to remain in place for parts of Central Otago until at least the middle of next week.
Roxburgh and Lake Roxburgh Village were put on boil-water notices on Wednesday, while Alexandra was added to the list on Thursday, following high water levels on the Clutha River.
Increased levels meant water supplies were at risk of containing harmful micro-organisms.
People in affected areas should bring tap water to a full rolling boil for one minute and then let it cool before using it.
A Central Otago District Council spokeswoman has also encouraged people to conserve water until the situation improved.
Roxburgh and Lake Roxburgh Village were put on boil-water notices at 5.30pm on Wednesday, while Alexandra was added to the list at 11am yesterday.
The announcements were made after tests showed the water supply to those towns potentially contained harmful micro-organisms, following high water levels on the Clutha River.
As a result, levels of silt were elevated, a council spokeswoman said.
"More rain is forecast, so we need to be cautious.
"Water from the river is entering the drinking water bore system, which makes it very hard to treat," she said.
Boiling water kills micro-organisms that can cause disease.
People should bring tap water to a full rolling boil, let it boil for one minute and then let it cool before using it.
" ... we ask you to make sure you are boiling all water used for drinking, food preparation and cooking, and cleaning your teeth until further notice.
"As well as boiling water, residents can help us by conserving their water use, with a particular focus on things like irrigation, car washing, laundry and dishwashers."
Water tankers will be in place this afternoon at the following locations in Alexandra: Poplar Grove, the St Gerard’s School car park in Killarney St, the car park near Molyneux Aquatic Centre in Boundary Rd and the Golden Block car park (behind Paper Plus) in Ventry St.
There are also water tankers in Roxburgh at Lake Roxburgh Village Hall and in Abbotsford St near Roxburgh Area School.
