This continuous cycle replenishes the groundwater. In groundwater flow the precipitation infiltrates the surface. The force that creates the infiltration is what is called hydraulic head. Hydraulic head is the sum of the water elevation between two points and the ratio of the fluid pressure to the unit weight of water. In the event that the layer confined you would find the hydraulic gradient which incorporates the sum of the elevation and the flow length.
Ground water flows from an area with high hydraulic head to an area with low hydraulic head.
The direction in which the water moves is based on the land conditions. The water moves down, horizontally, and vertically. Edward a. Keller's Environmental Geology Eighth Edition textbook.