A storm drain, storm sewer (US), stormwater drain (Australia and New Zealand) or drainage well system (UK) or simply a drain or drain system 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 fed by street gutters 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.

There are two main types of stormwater drain (storm sewer) inlets; side inlets and grated inlets. Side inlets are located adjacent to the curb (kerb) and rely on the ability of the opening under the backstone or lintel to capture flow. They are usually depressed at the invert of the channel to improve capture capacity. Grated inlets have gratings or grids to prevent large objects and debris from falling into the sewer system. However, their bars are fairly widely spaced so that the flow of water is not impeded. Consequently, many small objects can fall through.