Water is vital for the life and health of people and ecosystems, and is a basic condition for the development of countries. Water resources, and the related ecosystems which are sustained by water, are under threat from pollution, unsustainable use, land-use changes, climate changes and many other forces. This book incorporates basic and advanced information on all topics and issues relevant to the preservation of water resources quality. Its main strength lies in covering all aspects of water quality preservation, including: engineering hydrology, environmental and chemical aspects, quantitative (modeling approaches) and qualitative issues.