Water is indispensable to life, and the human body cannot do without it for more than two days. While historically it was abundant and freely available and plentiful, potable water is becoming a more and a more a scarce commodity, and increasing unequally distributed. The 20th century saw the transition from water gathering to water cultivation. The 21st Century will need to address a basic challenge: how to provide clean water to 7 billion people on Earth. It is a new field requiring a multidisciplinary approach and involving many other sciences: surface hydrology, climatology, geology, geography, physics, chemistry, biology, etc. This book takes a broad view, considers water as a single entity, and presents many examples illustrating the variety of existing hydrogeological problems and the diverse scientific, technical and social approaches used in resolving them. The book is intended primarily for students of Earth Sciences, Environmental Sciences and Physical Geography. It will also be useful for all players involved in water-related issues: hydrogeologists, geologists, soil scientists, agronomists, civil engineers, or developers.