Groundwater is an integral part of the water cycle and is linked directly with surface water. In the ACT, groundwater typically flows through fractured rock aquifers – currently thought to be relatively shallow and tending to mirror the topography of the catchments above them. Groundwater flows in a direction towards valley low points, with the water discharging into a stream. Aquifers represent an efficient water storage option because they do not lose water by evaporation as dams do.

Groundwater is used when bores are sunk. It can also be contaminated as pollution seeps into the soil and flows into the aquifers. Ecosystems that are dependent on groundwater need to be identified and managed.

Overuse of groundwater affects stream base flows. The time lag between pumping and detection of any effect presents a considerable risk for management and is the reason for ACT cautionary extraction limits and expanded groundwater monitoring.

The ACT groundwater monitoring program is a risk-based approach where aquifers with the most demand for abstraction and therefore at risk are afforded proportionally more resources for measuring and monitoring – aquifers in national parkland where no abstraction is occurring require minimal information to manage risk; aquifers in urban areas with higher use along with other changes to the catchment such as increased impervious surfaces require more information. More monitoring bores are located in aquifers in urban areas and a wide range of methods are used to determine sustainable yield.