Aucklanders have cut their water use by 35 million litres, or 8 per cent, in the last 24 hours - but it is still not enough to avoid the threat of having to boil water in the next few days.

Aucklanders have been asked to save 20l of water per person per day - or 50 million litres total.

Watercare chief executive Raveen Jaduram said the city used 415 million litres of water in the past 24 hours instead of the usual 450 million.

But this is still short of the target of 400 million litres a day, 11 per cent below normal - savings the company now says may have to continue for the next three weeks.


"It is essential that everyone reduces their water use until the end of the month," Jaduram said.

"Aucklanders have reduced their water consumption - which is great - but more savings are urgently needed.

"Everyone is being asked to Save 20. Watercare needs people to use 20 litres less water per day."

He said the target was "easily achievable".

"To put it in perspective, it's only a few minutes less in the shower and turning off the tap when brushing teeth," he said.

"Ardmore water treatment plant, which supplies up to two thirds of the Auckland region's water, is continuing to operate at half its capacity due to an unprecedented level of silt in the water coming from the Hunua dams.

"We are maximising production at our four other metropolitan plants which include those in Waikato and Huia.

"Currently we are meeting demand - none of our customers are without water - and the quality of the water has not been compromised. It's safe to drink straight from the tap.

"The situation at Ardmore is stable but if we can't achieve the targeted water usage savings we may be forced to release partially treated water into the region's supply. In such a situation, a boil water notice would be issued."

Last night saw approximately 100mm of rain fall in the Hunua Ranges and Waitakere Ranges, which is where nine of the city's water storage dams are located.

"The clarity of the water entering the Ardmore Water Treatment Plant is still about 100 times worse than what we would expect to see entering the plant," Jaduram said.

He said the call for savings applied to everyone connected to Auckland's metropolitan water supply network - those living as far south as Pukekohe and as far north as Waiwera.

Watercare tips to save water

1. Cut your shower time by two minutes: Approximate saving: 16 litres.

2. Turn off the tap when brushing your teeth. Approximate saving: 4 litres.

3. Only run your dishwasher when it's full.

4. Only run your washing machine when it's full.

5. Use the half-flush on your toilet.