Environmental water in a groundwater context is the water that supports groundwater dependent ecosystems (GDEs). GDEs can be either partially or fully dependent on groundwater at some point in their lifecycle. These ecosystems can include large areas such as rivers, creeks and wetlands where groundwater discharges to the surface as baseflow. They may also be smaller ecosystems such as springs or certain types of terrestrial vegetation such as River Red Gums where the root systems can access groundwater. Other GDEs are subterranean and are located within the aquifer itself, including cave ecosystems and stygofauna communities.
Groundwater environmental water can therefore take the form of the water left in an aquifer outside of the volume permitted for extraction; it may also be a part of surface water flow that groundwater contributes as baseflow to maintaining instream ecological values, or part of surface water environmental flows that becomes groundwater recharge. Protecting environmental water in the groundwater context then requires protection of the water in the aquifer and to those surface and groundwater resources connected to that aquifer. Protection may take the form of ensuring water quality is maintained or improved, that a groundwater level is maintained, or that a connection is maintained.
The Murray–Darling Basin Plan sets out requirements to ensure the protection of GDEs. Each state must then develop their Water Resource Plans (WRPs) to meet Basin Plan requirements. These requirements for groundwater environmental water include the protection of environmental watering in relation to GDEs, surface to groundwater connectivity, water quality and the structure and hydraulic relationships of aquifers.