Nitrate levels have risen in more than half of rural Canterbury water supplies over the past decade, according to a survey sampling groundwater from 358 wells.

Environment Canterbury's (ECan) 2025 Annual Groundwater Quality Survey found 38 wells, or 10.6%, had nitrate-nitrogen concentrations above the drinking water maximum acceptable value of 11.3 milligrams per litre, up on the 10% recorded in 2024.

Of the wells assessed for long-term trends, 59% showed increasing nitrate concentrations over the past decade, while 24% showed decreasing trends, with the remaining 17% showing no clear trend.

In September, ECan voted 9-7 to not proceed with any further investigation into funding for the treatment of private water supplies for nitrate contamination.

The decision effectively brought to an end a nitrate emergency, which the council had declared in September 2025.

But Greenpeace said the survey confirms Canterbury is still in a nitrate emergency, as nitrate contamination continues to rise in a majority of monitored wells across the region.

ECan water and land science manager Dr Elaine Moriarty said the results reinforced the importance of continued monitoring and testing of private water supplies, as well as sustained efforts to improve groundwater quality.

“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 the survey of 358 wells confirmed nitrates remained a long-term challenge.

Higher nitrate concentrations were usually found in areas with more intensive land use, ECan staff said.

Greenpeace programme director Niamh O’Flynn said the findings were not surprising.

“Despite the fact that thousands of rural Cantabrians can’t safely drink the water coming from their kitchen tap, the culprit - the intensive dairy industry - is still expanding in the region.”

ECan councillor Genevieve Robinson said the latest survey raised some serious questions.

She said the council’s own performance target is for at least 50% of monitored groundwater sites to show decreasing nitrate trends.

“Where are nitrogen reductions delivering measurable improvements? And when environmental performance targets are repeatedly missed, what changes? And who pays?

“We cannot keep measuring a problem without demonstrating meaningful progress towards solving it.”

But Dr Moriarty said actions to improve groundwater quality can take years to become visible.

“In parts of Canterbury with deep groundwater, the water we sample today may have entered the ground many years ago.

“This means changes in how land is managed may take a long time to show up in monitoring results.

“That's why annual surveys like this are so important.

“They help us track long-term trends, understand where risks remain, and provide communities with reliable information about the state of their groundwater.”

The survey also highlighted the connection between groundwater quality and the health of Canterbury's waterways, according to ECan staff.

More than half of the shallow groundwater samples assessed in areas connected to rivers and streams had nitrate concentrations above the surface water bottom line of 2.4 mg/L, meaning they could contribute to ecological impacts in surface water.

The report did have some good news, with the number of wells where E. coli was detected dropping from 49 in 2024 to 23 in 2025.

The survey also included a one-off assessment of lead concentrations.

Lead was detected in some samples at very low levels, but no wells exceeded the drinking water standard.

• LDR is local body journalism co-funded by RNZ and NZ On Air.