The top of the zone of saturation is known as the water table. The ground materials above this point are not saturated. Ground water behaves much like surface water in that it flows from high areas to lower areas. As it reaches these lowland areas, it often escapes to become surface water. This can occur in several ways.
Natural springs can exist in which the ground water simply breaks through to the surface.
It can also leak into streams and rivers. Many streams would become completely dry during periods of drought if it weren't for being constantly fed by the ground water which isn't as easily affected by surface weather conditions. Because of this tendency to flow downhill and the fact that water is constantly entering and leaving the ground water, the entire layer of ground water is in constant motion. Due to the fact that this water must move slowly through the rock and porous materials, it takes long periods of time for it to move, often as long as a day just to move a couple inches. In fact, ground water makes up about 95 percent of the planet' unfrozen fresh water supply.