Experts call for more water infrastructure investment as report reveals 'severe' pressure

Experts are calling for more investment in water infrastructure, after a report revealed the country averaged 31 wastewater overflows a day.

It showed there were "severe" pressures on water infrastructure, leading a third of councils to have at least one drinking water network with "very high" leakage levels by international standards.

Dr Mike Joy, a freshwater ecologist at the Victoria University of Wellington, said the report confirmed his concerns about water infrastructure.

"We've known for a long time that our wastewater systems are failing."

He said the network was run down and unfit to handle growing demand and strain from climate change.

"We're getting overflows, we're getting sewage going into the environment - and it's going to get worse because we have failed infrastructure."

Joy said water investment had been put off by local governments as it was not a "sexy" issue.

"It's not something that you get voted in on. It's not something that's popular and we have a lot of pressure on councils to reduce rates."

He said there needed to be stricter regulations and enforcement.

The report found that a fifth of wastewater treatment plants operated on expired consents; Joy said this was symptomatic of a lack of proper enforcement.

He said councils would be reluctant to fine plants which they owned themselves as it would effectively be a tax on ratepayers.

He said as a result there was no pressure on councils to address problems.

"They just get a sad face stamp from the authorities if they fail these things," he added.

The risk of failing infrastructure, he said, was the contamination of drinking water - which could spread disease.

During heavy rain and floods, rainwater could overflow into the sewage system, overloading the network.

"The treatment plant has no storage opportunity, so it has to just open the gate.

"And a lot of the water treatment - killing pathogens - happens with ultraviolet systems. And as soon as the water becomes too dirty or the flow's too high, they stop working and it's just discharging raw sewage into the environment."

Raw sewage could then find its way into drinking water catchments, he said.

"If we want to be able to swim in our beaches and rivers, then we have to make sure that we're not polluting them with human waste. It's really, really basic, really simple."

Industry group Water NZ said the report highlighted the need for more investment in water infrastructure.

Chief executive Gillian Blythe said councils needed to spend the money ringfenced for water projects under Local Water Done Well.

"It's critical that we understand the need to invest for our future climate, for our future populations and for the natural hazards that are faced across New Zealand," she said.

Looking to the future, she called for stronger protection of water drinking sources.

"Whether that's a river, a lake or an aquifer - because that is the most effective and most cost-efficient way to ensure reliable drinking water supplies for communities," she added.

She said protecting source water would cost less than having to treat contaminated drinking water.

Blythe said new water entities would play a vital role in addressing the "long-standing deficit" of water infrastructure.