20-year wait for better water possible as nitrate pollution worsens, experts warn

Tuesday, 8 October 2024

The region’s water quality may not see clear improvement for up to two decades, as the regional council warns things could get worse before they get better.

It comes as a new briefing by the Public Health Communication Centre warns Cantabrians face rising costs as nitrate levels increase.

The briefing’s authors - including University of Canterbury associate professor Tim Chambers, Otago University professor Michael Baker and research fellow Marnie Prickett - dubbed the severity of Canterbury’s nitrate pollution a “serious regulatory failure” that had “shifted the burden of pollution onto those downstream”.

They urged district councils to demand better protection of water sources, given they - and their residents - were left with the financial and heath costs of land use decisions by regional councils.

Nitrate, the most widespread contaminant in New Zealand’s drinking water, is colourless, odourless and tasteless. It comes primarily from intensified farming, which uses irrigation and synthetic nitrogen fertilisers to allow for more stock, resulting in large amounts of cow urine and fertiliser seeping into Canterbury’s stony soil.

The authors rejected Environment Canterbury’s (ECan) stance the nitrate problem was a legacy issue, saying their analysis of more than a decade of water policy showed the council could have used bylaws and planning to protect water or reduce pollution. They argue recent decisions were likely making the situation worse.

But ECan’s regulatory implementation general manager, Paul Hulse, said the problem dated back more than a century, and could take decades to improve.

“Degradation started 150 years ago when land use on the Canterbury Plains began to change.”

Due to the time it took for nitrate to travel through groundwater, “we can expect the situation to get worse before it gets better” in some cases, and the council did not expect to see clear improvements in groundwater for “at least another 15 to 20 years”, he said.

In 2017, when ECan placed restrictions on nutrient loads and even herd numbers, one farming leader predicted the region had reached “peak cow”.

That was more than 50,000 cows ago.

Canterbury’s dairy herd reached nearly 1.4 million in 2022-23, according to Stats NZ, its largest yet.

Those numbers were “not correct”, Hulse said.

He instead pointed to DairyNZ’s herd figures, which suggest Canterbury’s dairy herd was 940,527 in 2022-23, a reduction of 25,000 on 2021-22 (965,704).

The area under irrigation also increased, although ECan and Stats NZ again differed on figures.

The most recent figures ECan had were from 2020.

“When it comes to something as critical as people’s drinking water, we need to be really clear about what’s going on, and the source of statistics matters,” Prickett said.

It was “concerning” ECan was relying on a lobby group’s numbers over Stats NZ.

“You want to separate the regulator from the industry being regulated.”

The researchers could not access information on cattle distribution to know which catchments and sources were most at risk.

But those details needed to be available to the public and water suppliers such as district councils, she said.

ECan’s latest groundwater survey revealed faecal contamination in 9% of sites, nitrate levels over the maximum allowable value (MAV) of 11.3mg/L in 10%, and increasing nitrate levels in 59% of sites tested (compared to 1% over the MAV in 1992).

However, recent surface water analysis showed more sites were improving than worsening over the past decade, Hulse said.

While the highest nitrate levels were once relegated to private bores, rising levels in council controlled supplies have led some to look at alternative sources and methods of removing nitrate, which come with hefty price tags.

A 2022 report by consultants WSP and the University of Otago forecast the cost of denitrifying Christchurch’s water supply to be about $610 million for construction and $24m per year to operate.

The Selwyn District Council this year budgeted over $5m to search for alternative drinking water sources after high nitrate levels were found in town water supplies. It estimated long-term solutions could cost more than $400m.

Some campaigners argue New Zealand’s nitrate limit is too high for human and waterway health.

There was emerging evidence on health risks, such as pre-term birth issues and some cancers, and a precautionary approach was needed, she said.

“We should be heeding that, taking note … and not seeing 11.3 mg/L as a target.”

But it was not too late, Prickett stressed.

“The first step is to demonstrate categorically you're not worsening the situation, and I think ECan needs to do that.”