Nitrate levels still rising in most Canterbury wells

Almost 60 per cent of Canterbury wells are still recording increasing nitrate concentrations, a new groundwater survey shows.

The [www.ecan.govt.nz/get-involved/news-and-events/2026/groundwater-survey-highlights-ongoing-nitrate-challenge-despite-fewer-e-coli-detections Canterbury regional council survey], carried out in 2025, found nitrate levels exceeded the drinking water limit of 11.3mg/L in about 10 percent of the 358 wells tested.

In the Ashburton zone, almost 30 percent of wells exceeded the limit.

Regional council water and land science manager Elaine Moriarty said the results showed nitrate levels remained a long-term challenge in Canterbury.

"Groundwater is hugely important to Canterbury. It's the source of drinking water for many communities and it also feeds a lot of our lowland springs and streams," she said.

"There isn't any major change from last year that we can see in the numbers but change in groundwater is a long game and the actions on land often take between three to five years in some areas of Canterbury. In other areas with deeper groundwater the change is a lot longer."

On Friday, during a visit to Christchurch ahead of the election, the Green Party pledged to make it easier for people to check the safety of public drinking water supplies.

The Greens want to introduce a bill requiring the Water Services Authority to regularly publish drinking water quality data online.

Greens environment spokesperson Lan Pham said nitrate pollution came at a cost.

"Schools and communities are actually facing the costs of finding drinking water that isn't polluted by nitrates," she said.

"This is unacceptable. We want people to be empowered to know these things so they can put pressure on the right authorities, on government to actually turn the tide and protect our water at its source."

Greens co-leader Marama Davidson said up to 100,000 people fell ill each year from polluted drinking water.

"Nitrate pollution in our rivers is getting worse and it's costing ratepayers in Ashburton, Selwyn, Waimate, and Gore at least $17 million combined. Five schools in Otago, Canterbury, and Waikato have had to upgrade their water systems just so their children can have a safe drink of water at playtime," she said.

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.

Of the wells tested in Canterbury, 59 percent showed increasing nitrate concentrations, while 24 percent showed decreasing trends, with the remaining 17 per cent showing no clear trend.

The 2024 survey showed nitrate levels increasing in 62 percent of wells and about 10 percent of wells tested had nitrates above the drinking water limit.

Moriarty said they were a mix of public and privately-owned wells and not all were used for drinking water.

Nitrate levels could worsen before improving, she said.

"Environment Canterbury fully acknowledges it is a challenge for us and one that we are actively working with our community to support them with," she said.

The council said fewer wells showed evidence of E coli, with the number dropping from 49 in 2024 to 23 in 2025.

The survey also found more than half of the shallow groundwater tested near Canterbury waterways had nitrate levels above the environmental bottom line, posing a potential risk to rivers and streams.

Higher nitrate concentrations were found in areas around and downstream of intensive farming.

Federated Farmers president Colin Hurst said farmers were working hard to reduce nitrogen loss.

"The dairy farmers are reducing their stocking rates, planting the likes of plantain that has the ability to mop up some of the nitrogen, farmers are undertaking precision farming, so only applying the fertiliser where it's needed," he said.

"Farmers are fencing off their waterways and there are a lot of plants being planted in the waterways to reduce nitrates. It's going to take a little bit of time to sort these things out but we're on the journey."

DairyNZ general manager policy and government relations Roger Lincoln said Canterbury dairy farms had reduced nitrogen loss per hectare by 30 percent over the past decade.

Nationally, 97 percent of dairy farms had a farm environment plan, he said.

"DairyNZ, together with government and other partners, has invested $35 million over the past five years developing lower-nitrogen farming systems and this work continues," Lincoln said.

"A four-year Lincoln University farmlet trial found pastures containing an average of 17 percent plantain reduced annual nitrate leaching by around 33 percent, while maintaining milk production. We're working with farmers to translate that research into practical adoption on farm."

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 drinking water limit by almost 90 percent.

The ministry said it expected the review to be released by the end of this year.