Water security links together food, energy, climate, economic growth and human security threats. This publication sets out the challenge the world faces if nothing is done to improve water management in the next two decades. In nine chapters, it explores the sectors of agriculture, energy, trade, national security, cities, people, business, finance and climate. It is intended provide a background on the issue, presenting a selection of expert perspectives of the complex set of challenges faced by economies in managing future water needs in the next two decades. It also aims to highlight the implications of the challenges to social, economic and political well-being if no action is taken based on the current thinking on forecasts and growth trends. Importantly it also provides a platform to showcase some emerging approaches to tackling the problem including the initiative by the World Economic Forum among many others.The final three chapters of the publication turn attention on how to manage the water challenge in the next two decades. They explore breakthroughs in the development of a new economic fact base on water for governments, as well as looking at experiences in developing public-private coalitions that can encourage governments to take action on water. It also sets out a major next step for the World Economic Forum Water Initiative with the Water Resources Group.The publication concludes that governments can and must play a leadership role in setting frameworks for improved water management, but other stakeholders also do have a role to play in delivering solutions. It observes that many governments are now indicating their readiness to champion fact-based public-private-expert discussions.