Catchment Runoff can be directed to a groundwater node by dragging the Catchment Runoff symbol from the legend in the Schematic view to the particular node. A groundwater node can receive inflow from more than one Catchment, as well as other types of inflow input by Read from File or Expression methods (in contrast to Catchment Runoff designated as headflow to a river - other sources of headflow cannot be input for that river - see Catchment Runoff to Rivers).
If using the Soil Moisture (two-bucket) method to calculate Catchment Runoff, and Catchment Runoff is directed to a groundwater node from that Catchment, the Soil Moisture method becomes a "one-bucket" representation. (see Overview of Catchment Calculation Methods).
Catchments must contribute runoff to one and only river node, and optionally to one groundwater node.