Nowadays, the whole country is overrun by the water crisis. Therefore, rainwater harvesting is desired as an efficient alternative for water supplying. Before the execution of any rainwater harvesting project in rural or urban buildings, we need to prepare a comprehensive manual for designing and optimizing the water reservoirs. In this work, an inclusive plan was designed to study all parts of a rooftop catchment system, i.e. rooftop area, transferring equipments, reservoir and also water quality problem in Golestan province. Finally, a guideline was prepared for designing and optimizing the reservoirs with consideration of social and economic scopes in the study area. The methodology was based on the field surveying and questionnaire filling in 12 selected sites in Golestan province. Then, each site was hydrological simulated and reservoirs’ volumes were optimized based on the mass diagram approach. Water quality monitoring was carried out, as well. Finally, technical report was prepared and split into 7 parts including “introduction”, “literature review”, “study area”, “hydrological simulation and optimization”, “water quality”, “guideline” and “conclusion”.

Abstract
The crescent structure is one of the water harvesting systems that lacks precision in design, especially in the precision of intake volume of the crescent that may  cause damage. The study area includes sloped lands in which figs are grown through dry farming by using the runoff that is collected by the crescent structure. The purpose of this study is to optimize the dimensions of crescent pond structures in Estahban of Fars province. Therefore, a maximum of 24-hour rainfall data for 20 years (1995-2014) from the Estahban station was used in this study. After analyzing the data in terms of accuracy and homogeneity, the time series data were fitted to different functions and after selecting the best distribution function with respect to residual sum of squares, the maximum 24hour rainfall on different return period was calculated. Then, the SCS method was used for calculating the runoff and based on of the  100 square meters area of each micro catchment, the volume of runoff was calculated. The results showed that the use of the log Pearson type ΙΙΙ distribution parameters is the best compared with other functions. By selecting a return period of 10 years as the basis for design and considering the different slopes, the volume of the crescent structure must have a capacity exceeding 2.33 cubic meters in order to increase the likelihood of success for the project.