A rain garden is a shallow depression planted with native plants and grasses that is positioned near a source of runoff like a downspout or driveway. Rain gardens capture runoff, slowing pollutants and conserving water while improving water quality, recharging groundwater, and creating habitat for birds and insects. Runoff is considered bad because when rain hits impervious surfaces like driveways and concrete, it picks up pollutants and flows into sewer systems instead of soaking into the ground.