Stormwater is water that originates during precipitation events and snow/ice melt. Stormwater can soak into the soil, be held on the surface and evaporate, or runoff and end up in nearby streams, rivers, or other water bodies.
In natural landscapes such as forests, the soil absorbs much of the precipitation, 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, also known as flooding, and the other related to potential contaminants that the water is carrying or water pollution.