The world has made notable strides toward providing the poor with clean water and basic sanitation services over the past three decades. Since 1990, 2.6 billion people more people gained access to clean water for the first time. And yet, 663 million people remain without modern water services, including more than half of the rural population in 15 countries, mostly in Sub-Saharan Africa. Looking forward, a constellation of powerful forces—climate change, population growth, geopolitical conflict, and competition over scarce freshwater—threatens to undermine further progress, and even cause a historic reversal. This would be disastrous for the fight against diseases like cholera and malaria and the struggle for sustainable rural livelihoods. Bolstering state investment in water and sanitation infrastructure will remain essential, but will not be enough. Coordinated international action on climate change, conflict resolution, and sustainable water planning will be essential if we are to make the right to clean water a reality.