59% of rural Canterbury wells show rising nitrate levels

Nitrate concentrations are rising in 59 percent of rural Canterbury water supplies over the past decade. This finding comes from a survey that sampled groundwater from 358 wells across the region.

Environment Canterbury released its 2025 Annual Groundwater Quality Survey this week. The data shows that nitrate-nitrogen levels have increased in more than half of the sites where long-term trends were assessed. Conversely, 24 percent of those sites showed decreasing trends, while the remaining 17 percent displayed no clear direction.

The survey identified 38 wells, or 10.6 percent of the total, with nitrate-nitrogen concentrations above the maximum acceptable value for drinking water of 11.3 milligrams per litre. This percentage is higher than the 10 percent recorded in the 2024 survey.

The release of these figures follows a contentious vote by the Environment Canterbury council in September. By a margin of 9-7, councillors decided not to pursue further investigation into funding for the treatment of private water supplies affected by nitrate. That decision effectively ended a nitrate emergency that the council had declared in September 2025.

Greenpeace, however, argues that the emergency persists. Niamh O’Flynn, the organization’s programme director, stated that the findings were not surprising. She noted that thousands of rural residents cannot safely drink water from their taps while the intensive dairy industry, which she identified as the primary cause, continues to expand in the region.

Councillor Genevieve Robinson raised concerns about the council’s performance targets. The board aims for at least 50 percent of monitored groundwater sites to show decreasing nitrate trends. Robinson asked where nitrogen reductions are delivering measurable improvements and who pays when targets are repeatedly missed. She emphasized that the region cannot continue measuring a problem without showing progress toward a solution.

Dr Elaine Moriarty, ECan’s water and land science manager, explained that improvements can take years to appear in data. In areas with deep groundwater, the water sampled today may have entered the ground many years ago. This lag means changes in land management take a long time to show up in monitoring results. She said the annual surveys are essential for tracking these long-term trends and providing communities with reliable information.

The report indicated that higher nitrate concentrations are usually found in areas with more intensive land use. More than half of the shallow groundwater samples in areas connected to rivers and streams had nitrate levels above the surface water bottom line of 2.4 milligrams per litre. This suggests these sites could contribute to ecological impacts in surface water. The survey also found that the number of wells with E. coli dropped from 49 in 2024 to 23 in 2025. Lead was detected at low levels in some samples, but no wells exceeded the drinking water standard.