Hydrology for Sustainability is an accessible textbook introducing the movement of water through Earth’s interconnected systems. Written for undergraduate students and readers with little prior technical background, it explains the key processes of the hydrologic cycle, from clouds, rainfall, snow and ice to soils, groundwater, rivers, floods and droughts. Rather than presenting hydrology solely through equations or engineering tools, the book places water science within the wider context of environmental sustainability and human society. It shows how hydrologic knowledge can help us understand urgent challenges, including water scarcity, flooding, climate change, urbanization, groundwater depletion and the ecological impacts of water infrastructure. Clear explanations are paired with practical examples, technical boxes and global case studies. Topics include fog harvesting, rainwater collection, snowpack monitoring, soil-water processes, groundwater flow, watershed management, flood risk and hydrological modelling. The book also highlights Indigenous and local water knowledge alongside modern scientific methods. Engaging, interdisciplinary and solutions-oriented, this textbook is ideal for courses in hydrology, environmental science, sustainability, geography and water resource management.