Rainwater Harvesting System (RWHS) is a technique of water collection, which has been used since ancient times. A simple affordable, technically feasible and socially acceptable safe drinking water supply system in difficult geo-hydrological areas is very much in demand. RWHS can be considered as a probable solution of drinking water crisis in arsenic affected areas, saline zone in the coastal areas and areas prone to declining water table etc. Here, we have analyzed the rainfall characteristic of Bangladesh. In Bangladesh 85 percent of its annual rainfall during the monsoon and the average rainfall in a year is 2400 mm. Maximum rainfall is occurred in North-East, Chittagong and coastal zone and minimum in Western parts. Another important purpose of the study was to design Rain Water Harvesting System (Mainly the reservoir tank) as well as to determine the quality of water. Here we have designed software for calculating the size of the reservoir of RWHS. The water quality result shows that, 83 percent samples are free from faecal coliforms. Based on this discussion, Rainwater Harvesting System can become the most suitable solution for potable water.