The first national picture of water networks has revealed "severe" and "immense" pressures, with an average 31 wastewater overflows across New Zealand every day.

About a third of councils have at least one drinking water network with "very high" leakage levels by international standards, and water use has risen to an estimated 678 litres per connection per day.

Water services previously used to be regulated by the Ministry of Health, but the decision was made to set up a dedicated watchdog after the Havelock North campylobacter outbreak.

The then-Labour government set up the Water Services Authority (WSA) Taumata Arowai as part of its water reforms in 2020, and it was retained under the National-led government which backed the new regulator.

It's the regulator's third annual report on water networks, but the first that brings robust wastewater statistics into the picture, using data from across all 71 managed network operators, servicing 84 percent of the population.

It includes 559 public drinking water networks with 687 treatment plants and 56,000km of piping, as well as 331 public wastewater networks with 318 treatment plants and 35,000km of pipes.

In total, about 15 percent of those pipes were in "poor" or "very poor" condition - and that is likely an underestimate.

WSA head of systems, strategy and performance Dr Sara McFall said it showed a mixed picture of ongoing problems and some improvements - with wide variation across the country.

"A really important step forward for us [and] really important for the public ... because they now have better information about how their services are performing," McFall said.

"No one will be surprised to read that we have some pressures in the system with our infrastructure, and that's certainly come out."

She said with the councils' new Local Water Done Well organisations starting up and the Commerce Commission set to oversee pricing, New Zealand was now at an "inflection point".

Wastewater overflows and expired consents

The report showed 11,535 wastewater overflows in 2024/25, an average of 31 a day.

"We know they're going to happen, they're inevitable, but we would like to see interventions," McFall said.

"For instance, Watercare has just built their interceptor, which is a very large pipe which has already really helped with overflows," she said. "It will be good to see what that means for their overflow rates."

The problem was put down to a mix of capacity constraints - so not enough room in the pipes, particularly during bad weather - and blockages, and that data did not even include the Moa Point treatment plant failure in February which occurred after the reporting period.

"Blockages are largely caused by putting things down the sink or down the toilet that you shouldn't - so, wet wipes, fat, things like that," McFall said.

She said that was something the public could help prevent and the WSA had recommended public information campaigns.

That would be particularly helpful in metropolitan areas, which had nearly three times as many blockages per 100 metres of pipe compared to provincial and rural areas.

About 74 percent of wastewater was discharged to coastal environments, with about 99.6 percent of the wastewater produced in metropolitan areas treated to a high "tertiary" quality using advanced processes like filtration, nutrient renewal, and ultraviolet disinfection.

However, the report pointed to "widespread" non-compliance with consent conditions, noting 22 percent of treatment plants were operating on expired consents.

Nearly half of plants around the country (48 percent) were up for renewal within the next 10 years, and it took operators an average of five and a half years to get back up to date, some two decades.

"Pretty concerning," McFall said. "Which is why we've been putting in place these standards, which should standardise infrastructure, streamline the consenting, make it really consistent for people."

Those new national standards were set to come into place in the next couple of years, she said.

"We really would rather people were on modern consents and meeting environmental standards."

Drinking water leaks and overextraction

The report pointed to "uneven" drinking water performance across the country, with 32 percent of councils having at least one network in the "very inefficient" band of the International Leakage Index.

McFall said the international standard "has its critics" but it was good to have the numbers so leaks could be reduced.

"It's inefficient, obviously, and it's a waste, and that means you're taking more water from a water source than you necessarily need to. But it also has a potential for public health harm because if your water pressure is low... you can get contaminants getting into the pipes."

The report also noted that reducing leaks could help curb greenhouse gas emissions, because treating drinking and wastewater uses energy - so if less is wasted, and less is needed, less emissions are produced.

About 84 percent of drinking water pipes had been "graded" for condition, an improvement on the previous year's 81 percent, and much better than the 55 percent in 2022/23.

Concerningly, more than half the Defence Force network (56 percent) was in poor condition.

The report said rural operators were spending about half as much on new capital as on operations, and "may not be investing enough in renewing and replacing existing assets to address poor-performing networks".

Changing that could prove challenging, however, with rural areas spending about 2.9 times higher per person on average than in cities - with the proviso that spending data was not entirely reliable.

The report called for more consistent monitoring of network condition, saying 30 percent of the networks should be checked using CCTV every five years - but for now that figure was just 10 percent.

"You don't know what's down there unless you put something like a camera down through the pipes to really see what's under the ground. You don't want to be digging them up, and and it's quite hard to do this from a desktop exercise," McFall said.

And despite being easier to monitor, only three quarters of above-ground assets had been checked at all - falling short of the 78 percent of pipes checked.

Pipe conditions were typically better in provincial and rural areas with just 10 percent graded "poor" or "very poor" compared to 20 percent in cities, but cities were more up to date with monitoring.

Another problem was councils exceeding water take limits, with volumes reported for the first time.

Thames-Coromandel had the highest number of non-compliances - exceeding water take limits 14 times out of a total of 121 across the country, mostly in rural or provincial areas.

By volume, a total of 644,810 cubic metres of water was taken above what consents allow - the equivalent of 281 Olympic swimming pools - the largest proportion of that in Hauraki (43 percent) and Ashburton (38 percent).

Average household drinking water usage increased to 627 litres a day per connection, up from 604 litres last year, with rural usage per person nearly double that of the metropolitan centres.

What next?

The watchdog called for network operators to prioritise maintenance, invest where need was greatest, to meet regulations, fix assets in poor condition, tackle weather and capacity problems, reduce water loss, increase the use of water meters, and plan ahead.

Separately, the Commerce Commission would continue to investigate the quality and accuracy of the data and look at whether more transparency was needed.

The new Ministry of Cities, Environment, Regions and Transport would offer policy advice while the Auditor-General would continue to audit councils and council-controlled organisations.

The WSA said it also intended to set Network Environmental Performance Measures for stormwater, but till then the data available was limited.

"Stormwater systems are also more difficult to monitor than drinking water and wastewater networks because they are open, catchment-driven systems.

Their performance depends not only on built infrastructure, but also on land use, topography, ground conditions, receiving environments and how rainfall moves across the catchment.

"This makes it harder to isolate faults, measure performance consistently and compare results between operators."