This book contains selected peer-reviewed papers presented in the International Conference Down To Earth 2019, and is focused on Water Security and Sustainability. The topics covered in this book include sustainability of water resources, geospatial modelling and hydro-informatics, extreme hydrology (drought and flood), adaptation to climate-change impacts, vulnerability-risk-reliability-resilience, and hydrological risks in north-east India. The book also discusses innovative techniques and technologies for water resources assessment and management. Enriched with numerous case studies covering diverse topics, the book can be valuable for students, researchers, as well as industry professionals interested in water resources assessment, management and sustainable development.