A storm drain, storm sewer (US), surface water drain/sewer (UK), or stormwater drain (Australia and New Zealand) is designed to drain excess rain and ground water from impervious surfaces such as paved streets, car parks, parking lots, footpaths, 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. Even the gutters from houses and buildings can be connected to the Storm drain. Many storm drainage systems are designed to drain the storm water, untreated, into rivers or streams. As a result, it is not acceptable to pour certain types of chemicals into the drains.
Some storm drains lead to a mixing of stormwater (rainwater) with sewage, either intentionally – in the case of combined sewers – or unintentionally.

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