storm sewer

A storm drain, storm sewer, stormwater drain (Australia and New Zealand) or surface water system (UK) is designed to drain excess rain and ground water from paved streets, parking lots, sidewalks, and roofs. Storm drains vary in design from small residential dry wells to large municipal systems. They are present on most motorways, freeways and other busy roads, as well as towns in areas which experience heavy rainfall, flooding and coastal towns which experience regular storms.
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A system of pipes (separate from sanitary sewers) that carries water runoff from buildings and land surfaces.