​Downspout disconnection is the process of separating roof downspouts from the sewer system and redirecting roof runoff onto pervious surfaces, most commonly a lawn. This reduces the amount of directly connected impervious area in a drainage area. By redirecting this runoff, the amounts of Combined Sewage Overflow (CSO) events are greatly reduced. The concentration of pollutants from roofs is also reduced through this practice as the water is taken up by plants in the lawn.