Groundwater nitrate rates of change per year, 2004–2024

The colour scale indicates the annual rate of change relative to reference values for nitrate-nitrogen in New Zealand’s groundwaters.

The 0.0493 mg/L per year threshold is equal to 1/40th of the human impact reference value for nitrate-nitrogen (1.97 mg/L), and the 0.0985 mg/L per year threshold is equal to 1/20th; the 0.2820 mg/L per year threshold is equal to 1/40th of the maximum acceptable value for nitrate in New Zealand drinking water (11.3 mg/L nitrate-nitrogen), and the 0.5650 mg/L per year threshold is equal to 1/20th.

This figure appears in the Ministry for the Environment and Stats NZ Our Freshwater 2026 Tō Tātou Wai Māori environmental report.