This dissertation addresses the challenge of supplying water to rapidly growing cities in South Asia, using evidence from the water-scarce city of Chennai. Chennai (formerly Madras) is a rapidly growing metropolis of over 6.5 million people, whose infrastructure has not kept pace with its growing demand for water. In the year 2003-2004, Chennai experienced a severe water crisis: the piped supply for the entire city was virtually shut down for a 12-month period. Consumers became dependent on private tanker suppliers trucking in untreated groundwater from peri-urban areas. This research effort accomplished three goals: understanding the dynamics of the recent water crisis, extending the model to project the business-as-usual trajectory of Chennai's water supply and understanding how the trajectory may be altered by various policies. The study departs from previous research studies in several respects: Firstly, this study explicitly incorporates self-supply via private wells, and private-supply via the tanker market as an integral part of the urban water system. Secondly, the research integrates bio-physical and socio-economic behavior at multiple scales: user-scale supply and demand, utility-scale management, and basin-scale water availability and allocation. Finally, the study allows policy-makers to evaluate and compare a wide-range of policy options on an apples-to-apples basis, something that cannot be done with existing frameworks.