Groundwater quality in Tāmaki Makaurau: Annual data summary 2025

Author:

Laura Buckthought

Source:

Auckland Council Environmental Evaluation and Monitoring Unit, EEMU

Publication date:

2025

Topics:

Environment

Auckland Council's online interactive Water Quality and River Ecology Data Explorer presents State of the Environment (SoE) monitoring data for rivers, lakes, groundwater and the coast. Groundwater quality data can be compared across the region, between aquifers and over time.¹

This report provides a summary of groundwater quality monitoring results for July 2020 to June 2025.

Key messages

Nitrate contamination in some basalt aquifers

Nitrate concentrations were elevated in the shallow volcanic (basalt) aquifers and surface springs located in the wider Pukekohe area in South Auckland. In many cases, concentrations exceeded the Maximum Acceptable Value (MAV) for drinking water (11.3 mg NO₃-N/L). Further information on nitrate in drinking water can be found here: https://environment.govt.nz/assets/publications/Freshwater/risks-associated-with-nitrates-in-drinking-water.pdf

Stormwater inputs affect some basalt aquifers in urban areas

The water at shallow basalt sites in urban areas was well oxygenated. This suggests the aquifer is well connected to the surface. The urban sites also showed higher levels of indicator bacteria, dissolved phosphorus, nitrate (though not as high as South Auckland aquifers), soluble copper, sulphate and lower total hardness than other sites. These indicate the effect of stormwater discharges into the aquifer.

Higher levels of zinc at two Patumahoe sites

Soluble zinc concentrations were elevated at both of the two sites in Patumahoe Domain, with the Patumahoe Shallow (32m deep, in the Pukekohe basalt aquifer) site having much higher concentrations than the deep site (120m, in the Kaawa aquifer). This could suggest a contamination source or plume in the shallow aquifer that is slowly making its way down to the deeper aquifer.

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1. This does not include the detailed statistical analysis that is required to assess trends in water quality over time and is reported in our five-yearly State of the Environment reports.

Auckland Council, December 2025