This reduction was achieved by converting an impervious parking lot into a green building surrounded by green space and capturing the rain that falls on the site in a large cistern buried under the courtyard. This system collects rainwater from roof drains, channels the water through a high capacity filter in the courtyard, and stores it in an underground cistern. A drip irrigation system detects the amount of moisture in the soil so that plants are only watered as needed. When the irrigation system calls for water, pumps send water from the cistern through the irrigation system for distribution on-site. The cistern is sized to handle the average rainfall for the month of July (worst-case demand scenario). In addition to reducing the campus's use of potable water for irrigation, the quality of the stormwater runoff is also improved by filtering the water collected from the roof through the mechanical filtering provided by the capture system and the natural filtering provided by plants and other organisms in the soil.