Stormwater is basically a way of describing an accumulation of rainwater. This rainwater is either absorbed into porous surfaces like grass, forests, farm fields, and other areas of "open ground," or the rainwater collects on non-porous (or impervious) surfaces like streets, parking lots, and rooftops.
It's these impervious areas where rainwater collects that is the challenge for stormwater planners. In order to keep these impervious areas from flooding, streets, parking lots and buildings are often designed with underground pipes and basins that drain this stormwater.
Stormwater managers face three primary challenges:
Drain stormwater quickly in order to prevent flooding
Ensure stormwater is clean of contaminants picked up along the way
Use stormwater to recharge groundwater so that drinking water supplies will be available
In addition, these challenges must be accomplished taking into account existing infrastructure, working within limited space, and using a limited budget as economically as possible.