Rainwater harvesting system is mainly the process or a phenomenon of collection and conservation of rainwater from various techniques where the rainwater is the main source for the process of harvesting. Here we mainly consider the rooftop rainwater harvesting system for the collection of rainwater from roof or top of the buildings of Rajarajeswari College of Engineering campus. The study and implementation of the technique of rooftop rainwater harvesting system in RRCE campus mainly fulfill the needs and also resolves the issue of scarcity of water in all seasons by equivalent supply of collected and stored water for future needs . Also groundwater recharge could be done in efficient way. By implementation of this technique, water source will be increased up to 1420 meter cube in the campus which also intern could be used for construction works as well as maintenance of the good gardening works in the campus .Thus we can say it mainly fulfill the needs of scarcity of water and also mainly recharge groundwater