21 schools found with elevated drinking water nitrate levels

More than 20 schools have had drinking water with elevated nitrate levels above half the legal limit which has been linked to serious health outcomes.

A New Zealand study found an increased risk of premature birth at levels well below that, the College of Midwives recommends pregnant women avoid anything over five milligrams per litre, while international research links colorectal cancer to levels as low as one milligram per litre.

The 21 schools are mostly in Canterbury and Waikato.

In recent years five schools have breached the legal limit for nitrate of 11.3mg/L - Five Forks School in North Otago, Ashburton Borough School's rural Laghnor site, Te Kowhai, Harrisville and Te Wharekura o Te Rau Aroha in Waikato - with two topping 17 mg/L.

Upgrades to three of the schools' water supplies have been completed and work is underway at Ashburton's Laghnor site.

The Ministry of Education said it did not hold information on upgrades at Harrisville or Te Wharekura o Te Rau Aroha because the projects had been funded and managed by the schools themselves.

The ministry said upgrades at Five Forks School cost $47,900 and $36,000 at Te Kowhai School.

Green MP Lan Pham said it was unacceptable the costs were borne by schools, towns and taxpayers.

"What this data shows us is that it's not just Canterbury. We've got schools in the Bay of Plenty, Waikato, Hawke's Bay, Manawatu, Otago. This is an increasingly a New Zealand national issue."

Pham said politicians should explore some form of levy or polluter pays scheme, citing the millions of dollars the Ashburton District Council had allocated to manage rising nitrates in Tinwald, the $5m budgeted by Selwyn District Council in its search for a lower nitrate water source, and the estimated $400m Selwyn said it would cost for a long term solution.

"I think it's a really basic thing that people should be able to trust the quality of the water that comes out their taps, especially for our children in their most core place, at their school," she said.

The Ministry of Education would not confirm how many schools it was working with nationwide to address nitrate levels that were below the legal limit but still elevated.

A spokesperson said the ministry did not have data on school drinking water results with nitrate concentrations above half of the Maximum Acceptable Value (MAV) and was "unable to provide a verified national count of results at this time".

However, in response to a written parliamentary question from the Green Party in September, Education Minister Erica Stanford said 21 schools were known to have nitrate concentrations of 5.65mg/L or more:

• Ashburton Borough School (Laghmor site), Canterbury
• Carew Peel Forest School, Canterbury
• Galatea School, Bay of Plenty
• Harrisville School, Waikato
• Koputaroa School, Horowhenua
• Kōrakonui School, Waikato
• Lake Rerewhakaaitu School, Bay of Plenty
• Longbeach School, Canterbury
• Macraes Moonlight School, Waitaki
• Marotiri School, Waikato
• Pukehāmoamoa School, Hastings
• Pukehina School, Bay of Plenty
• Puketapu School, Hawke's Bay
• Riversdale School, Southland
• Tasman School, Tasman
• Te Kowhai School, Waikato
• Turakina School, Taranaki
• Waianiwa School, Southland
• Wainuioru School, Wairarapa
• Wairere School, Waikato
• Weedons School, Canterbury

Stanford responded to written questions stating she had not received any advice or briefings about schools that had upgraded their supplies because of high nitrate.

Critics of the official nitrate limit of 11.3mg/L, which is based on 1958 World Health Organisation guidelines, argue it is too high for human and waterway health.

Some scientific evidence suggests far lower levels pose an increased risk of pre-term birth and other reproductive risks. The New Zealand College of Midwives advises women to consider an alternative water source if nitrate is higher than 5mg/L.

In June RNZ revealed the Ministry of Health had quietly launched a review into the health effects of nitrate in drinking water after the Danish government reduced its nitrate drinking water limit by almost 90 percent.

Lincoln University adjunct professor Karyne Rogers co-authored the country's first nationwide survey of rural schools' drinking water, commissioned by the education and the environment ministries and published in 2024.

The study, which examined water at 245 rural schools, found more than a quarter had water that exceeded at least one of the drinking water standards.

Three schools had illegal levels of arsenic and another five had lead above the limit.

"We were seeing E coli popping up in more than 20 schools and things like lead and arsenic, which are heavy metals and highly insidious for young people to ingest," she said.

Results that did not breach legal limits were still concerning, Rodgers said.

"We're seeing more and more studies coming out of Europe that are recommending a tenth lower than the actual [nitrate] Maximum Acceptable Value," she said.

Rogers also co-authored a 2025 GNS Science study that tested 3800 rural drinking water supplies.

Researchers found five percent were over the legal limit, and another 31 percent were over half the limit.

The study used isotope testing to track the source of the nitrate pollution and identified dairy effluent as a primary cause.

Rogers said she wanted to see councils using the same tools to investigate the source of nitrate contamination.

"One of the few tools that can be done to understand and provide evidence - conclusive evidence - about the source is through the nitrate isotopes which will fingerprint the nitrate source, whether it's synthetic chemicals or animal waste or human waste or other causes," she said.

New Zealand Rural Schools Leadership Association president Andrew King said there had been positive moves to reduce the burden on schools that supplied their own drinking water and he hoped to see more.

"I think the biggest thing is making sure as many schools as possible are upgraded as quickly as possible and that schools are supported when things are not right," he said.

"For the moment it's the responsibility of someone in the school community to get that information to the lab monthly. There is a new self-testing kit available for schools, which the cost is covered, and is a much easier process to undertake rather than having to drive from a country school into town.

"It's just another thing to worry about and the irony is rural schools don't have the resourcing and the time to address it as easily as a larger school that would have a full-time caretaker or groundsperson who can do all the liaising that needs to happen with the experts."

Gus Gilmore, chief executive of the new School Property Agency, said 98 school and kura would receive full upgrades this financial year as part of the $30m Drinking Water in Schools programme.

The cost could "vary significantly" and depended on treatment requirements, existing infrastructure, school capacity and other factors.

He could not confirm whether the agency had plans to conduct further nationwide surveys.

Environment Minister Nicola Grigg said drinking water suppliers - in this case schools - were responsible for ensuring water was tested and met standards, and for providing safe and sufficient water to the communities they served.

She said regional councils managed land use and activities that could affect water quality at its source, subject to central government direction.

"Protecting drinking water sources is an important public health issue. Nitrate concentrations have increased in some parts of the country due to past decisions and practices and I am keeping a watching brief on this," she said.

Grigg said the government's new planning system would introduce limits for human health and better protection of drinking water sources.