Water crises are one the biggest challenges facing humanity in the 21st century. But what exactly is the nature of these crises? Scientists investigated the underlying causes driving water scarcity in 22 of the best studied cases across India, China, South America, Russia, and Australia using a quantitative technique that breaks down exhaustive case studies into measurable parameters. Srinivasan et al. show that in spite of the numerous ways in which humans interact with fresh water, each shortage or crisis is driven by one or more of eight underlying causes—which can be grouped into six “syndromes.” The authors found that just as declining natural supply can drive water shortages, so can human consumption or lack of proper policies.