ABSTRACT
Nature manages her water resources extremely efficiently with techniques for self-purification and for managing on a finite budget by recirculation of moisture. The recirculation technique is known as the hydrologie cycle, which is best explained diagrammatically (Figure 4.1). About 97 per cent of Earth’s water is stored in the oceans in a saline form. Almost the entire amount of fresh water is locked frozen in Antarctica and Greenland. A significant amount of the remainder lies at a considerable depth in the subsurface. The water that is normally available to us comes from the atmosphere, the land surface and the shallow subsurface; and constitutes an extremely small part of the total water inventory. Technologically it is feasible to acquire, process and utilize water from the oceans, ice sheets and deep underground, but the cost makes such efforts uneconomic. One of the favourite expressions in hydrology is that people expect water to be cheaper than dirt.
