Less than 1% of the earth's water is held as ground water. Ground water is water beneath the ground occupying space in the regolith and bedrock. It is equivalent to ...

1.) 40 times larger than all the streams or freshwater lakes combined

2.) 1/3 the size of the polar ice caps. (They can raise sea level by more than 100 feet if melted, so it is not an insubstantial amount.)

Most occurs within about 750 meters of the earths surface.

Zone of Aeration: the material below the soil layer than is permeable to the water. It provides a path for the water to migrate down to the water table.

Water may be present (after a rain) but is not permanent.

Saturation Zone: the upper surface of this zone defines the "water table" and it is the area which has constant water. The zone may fluctuate with the rainy season and rise or drop a small amount, but as long as the season is normal, the water stays fairly constant.

Capillary Layer: a small zone where water from the saturation zone is drawn upward via capillary action of the overlying sediment. This is the action of a liquid when in contact with a solid, and it tries to automatically wet the solids surface. Like water running up a paper towel.