The pollution of aquatic environment also reduces possible uses of water, especially those that require high quality standards i.e. for drinking purposes. This book discusses different problems regarding the quality of water and also focuses on the current techniques of water treatment. The primary emphasis is on sustainable choices of water usage that prevent water quality difficulties and aim at the protection of available water resources, and the development of the aquatic ecosystems. The focus is on the biological aspects of water quality using bioindices and biosensors.