The main aquifer systems in Northland are found in areas of basalt geology, such as Kaikohe and Whangarei, and in the Aupouri sands. Rainfall is the main source or recharge for the region's aquifers. NRC monitors groundwater resources via State of the Environment (SOE) and compliance assessment monitoring. Groundwater quality and quantity is measured, in addition to age testing and recharge estimates. This data allows NRC to understand how each aquifer functions and how much water is available for use.

In 2007-08, groundwater level monitoring was undertaken at 82 bores in Northland. Groundwater levels were found to be above average at most bores. Water quality testing was undertaken at 54 bores in the region. Major determinants in the majority of bores sampled were found to comply with the New Zealand drinking water standards. Specific groundwater investigations found areas of saline contamination at Ruawai; elevated nitrate levels at Taipa and bacterial contamination in the Russell aquifer.