What is a rain garden?

It's an ornamental garden that is designed to hold a few inches of water when it rains.  You can build one in your yard to receive roof downspout and hard surface runoff.  A MUNICIPAL rain garden is built in the street boulevard and holds some of the rainfall runoff from the street pavement.  When full (usually just a few inches) any additional runoff just continues on down the street.  Gardens are designed to allow the water to soak in quickly, within a day at most.  With enough rain gardens, we can improve the water quality of our local streams, lakes and rivers..

For more information, check out these sites:

Wikipedia definition of a rain garden

Virginia Department of Forestry info on rain gardens

City of Maplewood information on rain gardens