The central theme of this text concerns computational modelling methods for water, water near ions, water at interfaces, and water under other types of perturbations such as laser fields are described. Connections are made throughout the book with statistical mechanical theoretical methods on the one hand and with experimental data on the other. The book is expected to be useful not only for theorists and computer analysts interested in the physical, chemical, biological and geophysical aspects of water, but also for experimentalists in these fields.