This report is about water, the forgotten child of the climate change negotiations. The analysis reported here suggests that changes to water resources due to climate change will be strikingly uneven and unfair across the globe. They will jeopardize growth prospects in the regions worst affected and in some of the poorest countries. These challenges are not insurmountable, however, and smart policies that induce water-use efficiency, align incentives across regional and trading partners, and invest in adaptive technologies can go a long way toward reducing or eliminating these negative effects.