Rainwater harvesting is one of the most important techniques for collecting water. Harvesting and using rainfall runoff can help with better management of water resources. The purpose of this study was investigating the economy and potential of rainwater harvesting from the rooftops in Fasa University. Daily rainfall data for 30 years (1987-2016) at the Fasa station was collected and used to create monthly statistics. After analyzing the data in terms of accuracy and homogeneity, time series data were fitted to the different functions. After selecting the best distribution function with respect to the residual sum of squares, daily rainfall on 2 return periods was calculated. Using empirical equations and available parameters, the volume of the reservoir needed to store the harvestable water was determined. Finally, using the net present value, the time of return on capital and the economics of the project were studied. The results showed that the maximum volumes of water that can be harvested in daily precipitation is 24.6 m³, occurring in February. Therefore, according to the purpose and the selected method, we need reservoirs to store 24.6 cubic meters of harvested water. Also, the results of economic analyses showed that the return on investment of 250 million Rials occurred in the 6th year. Therefore, it is suggested that this project be implemented as a technical and economic plan at Fasa University.