Groundwater quality in Tāmaki Makaurau: Annual data summary 2024

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 2019 to June 2024.

Key findings

Nitrate contamination in some aquifers affects surface water

Nitrate concentrations continued to be high in the shallow volcanic (basalt) aquifers and surface springs located in the Pukekohe, Bombay and Glen brook areas. As this groundwater feeds the streams of the area, these streams also had high concentrations of nitrate.

Stormwater inputs affect some basalt aquifers in urban areas

The water at shallow basalt sites in urban areas and shallow unconfined basalt aquifers in South Auckland 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.

Groundwater variables are mostly stable, but there are some seasonal patterns in some aquifers

At most sites the groundwater quality did not vary considerably between seasons. However, some water quality parameters did show a rough seasonal pattern in some locations. For example, dissolved reactive phosphorus in the Fielding Rd Sand site was higher in summer than winter. The Patumahoe Spring site also showed more seasonal variation since it is exposed to the surface and more influenced by climatic variables.

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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, June 2025