In April 2013, DC Water and the DC Clean Rivers Project launched the Green Infrastructure Challenge, encouraging firms to design innovative green practices that absorb rainwater. These practices, known as Green Infrastructure, include: installing green roofs (gardens on rooftops), rain gardens, rain barrels, and pervious pavements; removing impervious surfaces; and using other natural means to capture and filtrate rainwater. Capturing the water before it can enter the combined sewer system will aid in alleviating combined sewer overflows (CSO) in the District.  DC Water and the DC Clean Rivers Project has put over $2 million dollars into this project.