Heavier than expected rainfall has made water in two river catchments in the Wellington region too dirty to treat, forcing the council to keep dipping into emergency supplies.
People in the region have been urged to conserve water and a ban on using water outdoors was put in place on Saturday to prevent a shortage in the capital following the extended dry spell.
Greater Wellington Regional Council has been taking 30 to 40 million litres of water a day from its emergency supply at the Te Marua lakes.
Several days of rain has not yet eased the problem. The council has not been able to treat water from the Wainuiomata and the Hutt river catchments because it has picked up too much surface dust from the heavy downpours.
The regional council's water supply manager, Chris Laidlow, says as soon as it stops raining, water at the two catchments will be able to be treated and could be ready as soon as Wednesday.
Mr Laidlow says water demand has decreased to 111 litres on Monday, the lowest for a single day since 1995.