A mayoral taskforce into Wellington's water woes has unanimously concluded the current approach is failing and major investment is needed to deal with decades of neglect.
The group was established in March, in the wake of major infrastructure failures, including the collapse of a wastewater pipe under the CBD.
The report, which has just been made public, reveals 30 percent of the capital's drinking water assets and 20 percent of its wastewater networks have already passed their use-by dates, while up to 60 percent of pipelines need to be replaced within 30 years.
Read the full Three Waters Taskforce Report (PDF, 7MB)
Mayor Andy Foster said as these assets aged they were becoming increasingly "prone to failure" and interim repairs were absorbing a greater amount of available funding, making less available for planned maintenance and renewals and increasing the risk of future problems.
"Couple this with the looming threat of climate change-related stresses on our water system from drought, high intensity rainfall and sea level rise and it is clear that there is urgency to take action now.
"If we do not act now, deferring these renewals and upgrades will lead to more burst pipes, more money being spent on unplanned reactive pipe repairs, more environmental pollution, and costly solutions such as hundred of millions of dollars for additional drinking water storage capacity."
The immediate priority would be to fund Wellington Water to investigate the actual condition of the underground assets to guide future investment.
The taskforce makes 48 recommendations, including ring-fencing rates collected for water to invest in infrastructure and handing over ownership of the assets to Wellington Water Ltd, which manages drinking water, wastewater and stormwater services for the region.
According to the report, the present accountability split is "unsustainable".
"The Taskforce's view is that asset ownership should be reviewed with a view to shifting assets into Wellington Water or a new stand-alone water services entity as is anticipated by central government."
Wellington City owns about $3.86 billion worth of three waters infrastructure, which is managed by Wellington Water.
Report highlights poor relationship between council and Wellington Water
Another report made public today - which was commissioned by the council's incoming chief executive Barbara McKerrow a year ago - has found the relationship between Wellington City Council and Wellington Water was so poor that their service contract was left unsigned for three years.
It showed council staff had little trust in the company, while Wellington Water was frustrated by the lack of engagement with senior management.
Tensions were so high neither party could agree on a services contract or an asset management plan.
In a joint statement, the two organisations say their relationship is now "collaborative and constructive".
In a preface to the mayoral taskforce report, iwi representatives from Taranaki Whānui and Ngāti Toa Rangatira said many people had "lost trust in our City Council, Wellington Water and the Greater Wellington Regional Council in terms of its ability to manage and look after our precious water assets and infrastructure for the people of today and most of all for our mokopuna of tomorrow.
"As mana whenua, we are left in no doubt that the political nature of local politics and local politicians has had an important part to play in the poor infrastructure decision making over many decades."
The taskforce representative from Ngāti Toa Rangatira, Hikitia Ropata, said the "divestment" in infrastructure was disappointing.
"I guess sometimes politics gets in the way of what investment really should look like."
The report was a strong signal to all citizens that fixing the water problems was going to cost: not just in terms of rates, "but in terms of time and effort to get things right".
Chief executive John Milford of Business Central - the Wellington Chamber of Commerce - who also sat on the taskforce, said everyone accepted the need to fund infrastructure "for our children and our children's children".
"The challenge we've got know is we've got to continue to fund that, but we've also got to fund for decades of underinvestment as well.
"So we're hit with a double-whammy."
Wellington Water wants $100m increase per year in capital investment
Wellington Water told the taskforce that the level of capital investment across the region, including Wellington City, needed to increase from around $140m per year to around $240m per year.
"Independent advice from the Water Industry Commission for Scotland suggests that even this increase will be insufficient, with $300m-$350m as a more realistic estimate. This represents a 200-250% increase on current levels."
Milford said it was "inevitable" that central government would have to help.
The major infrastructure fails - including the collapse of the tunnel under Dixon Street, which led to raw wastewater being discharged into the harbour, and the failure of the sludge pipes under Mt Albert which forced the council to spend $100,000 a day on trucks to take it to the dump - had a devastating impact on many businesses, and were also bad for the city's reputation, he said.