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Water is the ultimate source of entire life and for humans it is essential component not only for living but also for social, religious, cultural, economic and political reasons. Yet there is severe water crisis, both in terms of quantity and quality, facing the entire globe and the only reason suspected, which can lead to a third world war. There are many reasons for this situation which include inappropriate use of surface water resources, change in water usage pattern, change in hydrological cycle due to human intervention in nature, overexploitation of groundwater, wastages and pollution of both surface and groundwater resources. Some solutions, which can help ameliorate the situation, are judicious use of available resources, preventing pollution, techniques such as rainwater harvesting which include rejuvenation of traditional rainwater harvesting structures and employing alternate sources of water like seawater, gray water and treated sewage effluent. In this report, the technique of rainwater harvesting through rooftops in an urban scenario was looked into. The basic requirements, like the kind of data needed for doing such analysis and the challenges faced while employing the technique, were gathered by reviewing literature on the topic and the experiences from other case studies and success stories. The different aspects from which the problem can be viewed (modeling, law and policy, economic, etc) were also studied. The objective of the report is to study the effectiveness of rooftop rainwater harvesting in decreasing the gap between demand and supply with the help of two case studies. The methodology employed includes collection of rainfall data, finding out the area on which rainwater can be harvested for storage and subsequent reuse and calculating the volume of water that can be substituted with rainwater. At the end of the report, a basic design of a rooftop rainwater harvesting structure for the two cases was discussed along with some important considerations for making it.
