Water is a major input for the existence of life on the earth. Due to continuous increase in population, urbanization and industrialization, water is becoming scarce source in Pakistan. Moreover, recent severe drought has further accelerated the water shortage. The surface water shortage touched nearly 50% during the drought period. Water scarcity is a very vital issue in twin cities of Islamabad and Rawalpindi in Pakistan. With the passage of time, the water resources here are under enormous stress due to increased agricultural development, population growth and associated urbanization and industrialization. The gap between water demand and supply is expanding rapidly. In addition to this, water demand has considerably increased because of improvement in living standards. This resulted in an increasing pressure on underground water resources which lead to an alarming depletion of aquifers. This has emphasized the need to explore new water resources in Islamabad and Rawalpindi. The objective of this research paper is to find out rainwater harvesting potential in the twin cities and evaluate its suitability for supplement water supply and other miscellaneous uses such as ground water recharge and control flooding of Nullah Lai (the city main drain). Which in turn to overcome water demand to some extend, recharge our depleting ground water resources and development of an additional source of water within the twin cities.