Auckland Mayor Phil Goff is inspecting the flooding aftermath in New Lynn this afternoon after calling for more safeguards to the city's water supply.
Goff will visit the West Auckland suburb, held up as a poster child for housing intensification, where the stormwater infrastructure failed to cope with yesterday's rain bomb, flooding flats, shops and opening up a huge sinkhole.
Speaking on Radio NZ's Morning Report, Goff said the city had to build more resilience into the water system.
I know they say it is a one in a 100-year event, but there is no guarantee with global warming that we are not going to a have a whole lot of these events
Despite the rains being an extraordinary event, a world-class city such as Auckland should have high-quality, safe drinking water at all times, Goff said.
Auckland households face water restrictions until the end of the month despite hitting savings targets.
Aucklanders' daily water consumption has dropped to 382 million litres, well within the necessary range of 400 million litres or fewer.
Watercare congratulated residents but warned that if savings did not continue, partially treated water might need to be released into the system and then people would have to boil water.
Goff said the city had to look at stopping silt getting into the dams in the Hunua Ranges, which supply water to the Ardmore water treatment plant.
"We have got a concern that two-thirds of the water treated comes through the Ardmore water treatment station. That's a lot of eggs in one basket," Goff said.
He said Watercare was renewing the Huia water treatment plant and seeking extra capacity from the Waikato River and other engineering options were needed for treating water.
Goff said with Auckland growing at 45,000 people a year, it reduced the headroom when an emergency occurs.
"I know they say it is a one in a 100-year event, but there is no guarantee with global warming that we are not going to a have a whole lot of these events," he said.
The Green Party said extreme flooding in Auckland shows the urgent need for central government-led investment into ageing infrastructure to prepare for more frequent and extreme weather events.
It has been forecast that the capacity of Auckland's stormwater systems may be exceeded more frequently in future because of climate change-induced heavy rainfall events, according to the Ministry for the Environment.
"There is a real risk flooding on this scale will happen more frequently if the Government doesn't start supporting cities to upgrade stormwater infrastructure now," said Green Party co-leader James Shaw.
"Upgrading a stormwater pipe is never going to be as sexy as opening a new highway, but we've seen the consequences of not doing it. People's homes and businesses are wrecked and sections of the city are cut off.
"Auckland, like most of our cities, has incredibly old stormwater systems that urgently need upgrading.
"Council budgets are already stretched so either Government funding or a new funding mechanism is needed to help them do this," he said.