The report analyzes the nature and scale of the global water challenge and proposes solutions to close the demand/supply gap. It ranks the solutions on the basis of cost, and produces a "water cost curve," that can be used by policy makers as well as investors, to arrive at low-cost solutions to water security. In-depth studies were conducted in four countries/regions facing challenges in the water sector - China, India, South Africa and Brazil - and in each country, the potential measures to close the gap between demand and supply was evaluated.