Water is the most essential resource of all life on Earth. The spatial and temporal distribution of water is highly variable and is dependent upon the climatic factors that are beyond human control. Water resource systems are an important part of the infra-structure of every country, particularly the developing ones. In addition to the basic purpose of supporting life, water resource systems serve a multitude of water uses such as water supply, hydropower generation, recreation, irrigation, flood control, navigation and wild life maintenance. Due to tremendous population growth and extensive industrial and agricultural development, the demand on water resources is increasing everywhere in the world. In some parts, the characteristics of water supply and demand pose few problems for agricultural, domestic, and industrial users. In other areas, including much of the developing world, physical, social and political factors make effective water resource management vital. The situation is critical in developing countries as the gap between water demand and supply has been continuously widening. This has led to an increased emphasis on the optimal management of the available resources.