The 21^st century is witnessing the collision of two powerful trends—rising human populations coupled with a changing climate. With population growth, the demand for water is growing exponentially while climate change is making rainfall more erratic and less predictable. Current water management policies are outdated and struggle to address these challenges. If the policy status quo persists, water scarcity will proliferate across new regions of the world and intensify in areas where water is already scarce. This will have far reaching human and economic implications. Water is not only a declared human right, necessary for life and health, but is also a key input into the global economy, powering manufacturing, turning energy turbines, and nourishing crops and livestock. The way in which water is managed in the face of these growing challenges will be key to the economic success of countries where it is scarce and will almost certainly determine whether the world meets its ambitious Sustainable Development Goals.