New research into the effects of climate change says New Zealand's drainage systems need a major and expensive upgrade if they're to cope.
It's likely to cost ratepayers billions - but the report says if it's not carried out we're in for serious problems.
We're already seeing signs of what's to come. In March the Auckland suburb of New Lynn was underwater after a massive deluge flooded streets and storm water systems were overwhelmed.
And the research shows water networks like these will soon be under even more pressure.
"We need to start to transition our infrastructure to a model that's more appropriate for the weather patterns and sea level rise that we can expect," says University of Waikato Professor of Environmental Planning Iain White.
The Deep South report found we can soon expect higher sea levels leading to increased sewage overflows and salt water corrosion in pipes.
More frequent coastal storms causing inundation, physical damage and treatment plant failures - as well as extreme rainfall and droughts.
"We need to start thinking about what future weather patterns are like and to adapt and prepare in advance because it we adapt now we'll actually save money going forward," says Prof White.
But it won't come cheap. New Zealand's waste and storm water systems are valued at over $20 billion.
To upgrade and replace could cost even more than that. So, who's paying?
"Ratepayers are going to pay for it, there may be some central government assistance but that seems unlikely it's effectively a local council problem," says Water New Zealand CEO John Pfahlert.
But officials warn that if nothing's done it'll cost even more.
This year has already seen devastating weather events cause havoc in Edgecumbe and Otago.
Figures show weather related claims are now at the highest since records began with more than $230 million paid out this year.
"This is about understanding risk and then in a grown-up way managing it well and tries to keep costs as low as we can, but more importantly keeps communities together," says Local Government New Zealand CEO Malcolm Alexander.
Researchers say more work needs to be done to identify the most vulnerable areas.
But communities like these will be hoping others act - so they avoid the same disasters, in coming years.