Water at the surface of the earth.

The water beneath the Earth's surface.

The change of state from a gas to a liquid.

Rain, snow, sleet, or hail that falls from clouds to the Earth's surface.

The continuous movement of water between the Earth and its atmosphere.

The downward movement of water through soil and rock due to gravity.

A rock layer that stores ground water and allows it to flow.

The region of land drained by a river system.

Vaporization that occurs at the surface of a liquid below the liquid's boiling point.

An underground boundary where the zone of aeration and the zone of saturation meet.