Water can create peace or spark conflict. When water is scarce or polluted, or when people have unequal, or no access, tensions can rise between communities and countries. More than 3 billion people worldwide depend on water that crosses national borders. Yet, only 24 countries have cooperation agreements for all their shared water. As climate change impacts increase, and populations grow, there is an urgent need, within and between countries, to unite around protecting and conserving our most precious resource. Public health and prosperity, food and energy systems, economic productivity and environmental integrity all rely on a well-functioning and equitably managed water cycle.