Although many theoretical developments have been achieved in recent years, the progress both in understanding and application of risk and reliability analysis in water resources and environmental engineering remains slow. One of the reasons seems to be the lack of training of engineers with phenomena of statistical nature, including optimum cost and benefit decisions under uncertainty. This book presents, in a unified and comprehensive framework, the various aspects of risk and reliability in bothwater quantity and quality problems. The topics covered include uncertainty analysis of water quantity and quality data, stochastic simulation of hydrosystems, decision theory under uncertaintyand case studies. Methods for risk analysis of extremes in hydrology, groundwater clean-up, river and coastal pollution as well as total risk management are presented.