A watershed is a geographic area of land in which all surface and ground water flows downhill to common point, such as a river, stream, pond, lake, wetland, or estuary.
A watershed is also known as a basin.
Stormwater is water that originates during precipitation events and snow/ice melt. Stormwater can soak into the soil (infiltrate), be held on the surface and evaporate, or runoff and end up in nearby streams, rivers, or other water bodies (surface water).
In natural landscapes such as prairies or forests, the soil absorbs much of the stormwater and plants help hold stormwater close to where it falls. In developed environments, unmanaged stormwater can create two major issues: one related to the volume and timing of runoff water (flooding) and the other related to potential contaminants that the water is carrying, i.e. water pollution.
Stormwater is also a resource and ever growing in importance as the world’s human population demand exceeds the availability of readily available water. Techniques of stormwater harvesting with point source water management and purification can potentially make urban environments self-sustaining in terms of water.