What is Watershed ?
Watershed is an area that contributes its total run off through a common/single outlet .The term is not restricted to surface water runoff and includes interactions with subsurface water. Watersheds vary from the largest river basins to just acres or less in size. A high percentage of the water that originates in the watershed as precipitation – rain and snow – is retained as groundwater. 95% of the fresh water in the world is retained as groundwater. Groundwater moves more slowly than surface runoff, but it is in motion. Moving even more slowly is groundwater contained in aquifers, underground areas covered by low-porosity caps.