Auckland officials want to fast-track moves to take more water from the Waikato River, to stave off the threat of a regional water shortage.
Residents are being urged to take shorter showers as reservoir levels drop after unseasonably warm conditions and six months of below-average rainfall.
Despite the belated arrival of winter rain, total storage is sitting at almost 60 per cent of capacity. The historic average for June is 84 per cent.
An existing resource consent allows up to 150,000 cubic metres of Waikato water a day to be fed to the Auckland supply network.
In 2013, Watercare — the Auckland Council-owned water supply company — asked the Waikato Regional Council for permission to lift that to 200,000 cubic metres.
Last night, Auckland mayor Phil Goff said they were still waiting for a decision.
"They have taken some time to process it so we will probably need to hurry that up."
A Watercare spokeswoman said the Waikato had been part of Auckland's water supply network since 2002.
The river had provided an average of 37,000 cubic metres of water to the region each day but the number fluctuated.
The organisation was closely monitoring "the dry weather situation" and "carefully balancing" multiple water sources, she said.
"At the moment we are maximising production from our river and aquifer sources to reduce demand on our dams," said head of water value Roseline Klein.
Compounding the threat to Auckland's water supply, in the short-term at least, was yesterday's leak of huge amounts of raw sewage into Lake Taupō, which feeds the Waikato.
Taupō District Council chief executive Gareth Green last night said multiple councils, including the Auckland Council, had been notified to stop taking water from the Waikato.
A Watercare spokeswoman said she did not believe there was cause for concern.
The prolonged dry period has already started to bite for people with water tanks on the edge of Auckland's urban sprawl and in rural areas to the north.
"The volume of water supplied to water tanker operators over the first six months of this year is over four times greater than last year," Klein said.
"In practical terms, we've filled over 19,000 more water tankers. What this shows is the correlation between the weather and demand."
MetService meteorologist Sarah Haddon said the Auckland region will experience showers today but it will have little significant impact on reservoir levels.
Goff said Watercare was right to give Aucklanders early warning of a possible shortage.
"Say there is an extraordinary event and the ultra-dry period continues through to spring and summer, that would put us under much greater pressure," he said.
"Let's just take the small measures now that we need to save a lot of water and we'll get through it fine."
The last time mandatory water restrictions were imposed in Auckland was in 1993/94.
5 top tips for being waterwise this winter
• Turn off the tap when brushing your teeth or shaving.
• Try to shower for four minutes or less.
• When hand-washing dishes, fill the sink rather than washing the dishes under a running tap.
• Wash full loads of laundry whenever possible. This will save water and energy.
• Check to make sure your toilet cistern isn't leaking.