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Rain Barrel

A small storage device that collects stormwater usually from a roof surface.

Also known as a Garden Barrel.

Rain Garden

A planted depression or a hole that allows rainwater runoff from impervious urban areas, like roofs, driveways, walkways, parking lots, and compacted lawn areas, the opportunity to be absorbed.


MSD's Green Infrastructure initiatives - combining plantings, water features, and other activities that manage stormwater as close as possible to where it falls; slowing it down so it can be absorbed by the soil and/or plants.

Also known as Constructed Wetland.

Rainwater Harvesting

The collection or capture of rainwater on-site, rather than allowing it to run off.



Raw Sewage

Plant influent or wastewater before any treatment.

Receiving Waters

Bodies of water or surface water systems that receive water from upstream sources.


The part of the precipitation falling on a drainage area which does not escape as surface stream flow. It is the difference between total precipitation and total runoff during the period, and surface or underground storage onsite.

Retention Basin Wet Pond

A stormwater control structure with a permanent pool of water into which storm runoff is directed. Runoff from each storm is retained, allowing suspended sediment particles and associated pollutants to settle out. Water in the basin infiltrates or is displaced by runoff from a subsequent storm.

Retention Practices

Techniques that hold or retain runoff water, allowing it to infiltrate, evaporate, and/or be used on-site in order to reduce off-site transportation of runoff and improve water quality.


Right of way


Excess rainfall, snowmelt, or irrigation water that flows over the surface of the land. It will eventually infiltrate to the ground, evaporate, or flow into a storm drain system, stream, river, lake, or other waterbody.