A storm 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 streets and freeways, as well as towns in areas which experience heavy rainfall and flooding. Many storm drainage systems are designed to drain the storm water, untreated, into rivers or streams.

Storm drain lines need to be cleaned regularly. Routine cleaning reduces the amount of pollutants, trash, and debris both in the storm drain system and in receiving waters. Clogged drains and storm drain inlets can cause the drains to overflow, leading to increased pollution and erosion. Cleaning reduces the amount of debris and sand in particular, that can settle at the bottom of the big diameter pipes, reducing the capacity to efficiently carry the runoff water in a rain event.

Areas with relatively flat grades or low flows should be given special attention because they rarely achieve high enough flows to flush themselves.

Leaves, sticks, cans, bottles, bags and other large debris can infiltrate a storm system through gutter grates. Significant amounts of sand and gravel can also build up on the bottom of storm lines. The accumulated debris prevents the storm water from draining effectively, causing backups that flood streets.