A rain garden is a garden with a shallow depression that captures runoff from impervious surfaces, such as rooftops, patios, driveways, and parking lots, before it enters the storm water system. Rain gardens can be customized and are limited only by the resources and time you want to put into them. They use natural processes to improve water quality by filtering pollutants and reducing the amount of stormwater runoff. The water easily infiltrates into the soil because of the deep roots of the native plants and recharges the groundwater supply.