Book excerpt: Global water crisis is a challenge to the security, political stability and environmental sustainability of developing nations and with climate, economically and politically, induces migrations also for the developed ones. Currently, the urban population is 54% with prospects that by the end of 2050 and 2100 66% and 80%, respectively, of the world's population will live in urban environment. Untreated water abstracted from polluted resources and destructed ecosystems as well as discharge of untreated waste water is the cause of health problems and death for millions around the globe. Competition for water is wide among agriculture, industry, power companies and recreational tourism as well as nature habitats. Climate changes are a major threat to the water resources. This book intends to provide the reader with a comprehensive overview of the current state of the art in integrated assessment of water resource management in the urbanizing world, which is a foundation to develop society with secure water availability, food market stability and ecosystem preservation.