This report addresses a critical issue facing mayors in cities around the world: access to clean and adequate water supplies. The growth of urban populations, coupled with incidences of sudden climate stress and long-term land degradation of drinking watersheds, pose increasing risks to urban water supply with serious implications for the future health and well-being of urban residents. Without water, cities cannot thrive. Accompanying this report is the Urban Water Blueprint online tool that analyzes the state of water in more than 2,000 watersheds and 530 cities worldwide to provide science-based recommendations for natural solutions that can be integrated alongside traditional infrastructure to improve water quality.