The most important part of the watershed is the water cycle that drains and fills the area. This cycle is identical around the world. The global water cycle is a continuous process of water movement. The total amount of water involved in this cycle never changes however, only the form of its existence: liquid, solid, or gas. Solar energy pushes the cycle by creating heat that evaporates water from oceans, lakes, streams, and even plants. (Transpiration is the special name given to water evaporated from plants.) The now gaseous water vapor rises to the atmosphere and condenses around dust particles into clouds. The clouds gradually increase in size and weight until too much water is accumulated and precipitation begins. The rain or snow brings the condensed water back to earth to soak into the ground and refill the oceans and lakes.
Water that enters the ground is said to infiltrate or percolate into the soil. This water may either be stored as part of the ground water if it reaches the saturation zone (where all of the space between rock particles is filled with water) or may flow through the ground to empty into a stream or lake.
**put in pic of water cycle here**