Water is an essential commodity for all living beings: for direct consumption to sustain life and health, for indirect consumption through water required to grow food, fodder and fibers. Whereas the sources of water are depleting in comparison to increasing demand as a result of growing population in Kathmandu valley including other city areas. The pressure on water demand is escalating with the annual population growth rate of 4.4%. Presently the water demand of Kathmandu valley reached to 320 MLD in response to supply of 118.4 MLD in monsoon and only 68.8 MLD in dry season with 20% losses from the leakages. KUKL; an authorized institution to supply water, have no reliable alternative sources other than to extract ground water in order to lower this gap between growing water demand and limited supply except than to wait for Melamchi project. In such situation, this study has analyzed the potential and possibilities of rooftop RWHS in urban context for its wider promotion and acceptance. The analysis of Hydrological data of Kathmandu shows a huge potentiality of rooftop rainwater harvesting.