Climate change and overpopulation make it tough for cities to provide water. But these urban centers are leading the fight for a sustainable future.

Earth's rising temperature and growing population are putting tremendous stress on the water system, particularly in urban areas. Affluent cities still need to address climate change effectively, while developing countries have trouble providing enough potable water to their growing citizenry. Fortunately, some cities are leading the way and taking steps to show us a sustainable future. This article explores the principles they follow and highlights some of their success stories.