A watershed is any area of land where water falls, flows and drains into a common lower outlet such as a river or lake. It can be as small as a puddle or as large as an area where all the water from the land goes to the same point.
A watershed is commonly known as a rainfall or precipitation collector. It collects water from the highest point, also called the headwater, and delivers the water through tributary streams to a larger water basin or a mouth, such as a river. One of the more well-known watersheds is the Sierra Nevada watershed, which supplies water not only to more than half of California and Northwestern Nevada's population, but also supports and provides premium habitat to the wildlife in the mountain area.
Not all water that flows through the watershed flows down to lower water channels. When the surface of the watershed area is dry, some of the precipitation may permeate the soil, move downhill and enter the stream bank. Some rainfall, however, can go deeper and replenish the ground water aquifers. The amount of water that can infiltrate the soil also depends on the soil's characteristics, the saturation point and the overall cover of the land.
The amount of water collected and delivered to a larger catch basin is further lessened by residential and commercial use. The water flowing through the tributary streams is often utilized to irrigate farms and lawns and to supply drinking water to the population and other industries.