A rain garden is a garden designed to capture water and allow it to infiltrate into the ground. Some rain gardens are constructed to infiltrate water runoff from roof downspouts—these enable you to disconnect your roof downspout from the city storm water system and utilize that water in your own yard. Others help to deal with pooling in yards by redirecting the water into an area of good infiltration. Rain gardens are not meant to contain standing water—they should drain within 24-48 hours of a large rainfall.