Rapid urbanization of cities includes common characteristics of high-density populations and large number of impervious surfaces. The high percentages of impervious surfaces like rooftops, roads and parking lots in dense cities would block the natural hydrological infiltration process and increasing flooding threats. The goal of this study is finding solutions for meeting the nonpotable water use demand by applying water harvesting while also creating open green spaces for residents in urban communities. The design thesis explored the level of benefits that can be achieved by harvesting water from impervious surfaces like rooftops to fulfill the need for water consumption, purification and green open spaces for social activities in residential high-rise condominiums (multi-family residences) in Wuhan, China. The study has compared hydrological and social benefits from 3 different design scenarios in the selected urban community: 1) the existing site design with underground parking, 2) a new design without underground parking which expands water harvesting options, and 3) a new design with underground parking which limits the application of some BMPs (Best Management Practices). This study used open space design and water harvesting as a strategy to meet 94% of non-potable water consumption by harvesting water from residential rooftops as well as to decrease and purify surface runoff to reduce the flooding threat from ground surfaces in the selected community. The proposed open space design also achieved social benefits of providing places for social interactions, supporting various recreational activities, educating children about environmental issues while having in outdoor activities, experiencing nature and keeping or improving the physical and mental well-being of people in the selected urban community. / Master of Landscape Architecture / Dense cities have the characteristics of having high-density impervious surfaces roads, bridges, rooftops as well as a large amount of population. Since a large amount of increasing population in dense cities would result in high demands for water consumption, the water shortage problem, as a global issue, has challenged the distribution of water resources in dense cities. The massive number of impervious surfaces, as a result of rapid urbanization, have blocked the process of hydrological circulation by making natural infiltration impossible. Therefore, many dense cities are facing the challenges of waterlogging or flooding threat and the decreasing amount of water resources. This study focuses on using open space design and water harvesting as a strategy to relieve the stress of limited water resources and waterlogging or flooding threat in dense cities. This thesis has chosen an urban community in Wuhan, China for making open space design and bring the hydrologic and social benefits to the selected urban community by combing the practices of water treatment into the design. The new open design in the selected community not only has the hydrological benefits of decreasing and purifying surface runoff to reduce flooding threat, but also has many social benefits such as providing places for social interactions, supporting various of recreational activities, educating children about environmental issues while participating in outdoor activities, experience nature and keeping or improving the physical and mental well-being of people.