Water scarcity is a major problem in developing countries. Rain water has been valued for their purity and flexibility. Rainwater, resolutions on the merits of the gathering, transmission and storage of rain water there. The scope and limits, methods, technology, complexity System, goals and other usages a change in the level of rain water for parts of irrigation. They are in urban areas. Large-scale rainwater collected there for all households. Reducing groundwater resources, poor quality of some of groundwater, rainwater collection system flexible and modern methods of treatment of the most important reasons for gathering rain water for domestic usages respectively. (RWH) is a technology in which surface runoff effectively during rainy periods can be efficiently collected. In order to support by technology systems (RWH) have the necessary skills, materials and equipment to be seen. After that rain water harvesting for rainfed agriculture or to supply used for household purposes. Intermediate methods and simplified methods of estimating the size of the reservoir in the case are simple

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