Throughout human history, water has been a source of life as well as of death. Water is so common a natural resource that its availability is taken for granted. An adequate quantity of water for meeting basic human needs is a prerequisite for existence, health, and development. As development proceeds, the demand for water will invariably increase. Despite our understanding about the vitality of water for development, and its crucial role in meeting basic human needs, we continued with our extravagant water-use patterns as if the availability of fresh water on the planet is unlimited.
Fortunately for the human race, the unsustainable nature of water-use patterns, despite modern technology and feats of engineering, has been dawning upon us for the last decade or so. Water planners in many corners of the world are projecting that within two decades, availability of freshwater sources will fall short of needs. Water is mostly taken from rivers or aquifers. Water that has been withdrawn, used for some purpose, and returned to the environment will be polluted, making it unfit for further beneficial uses. In many countries, a large proportion of such polluted water (i.e. wastewater), is discharged into the environment with little or no treatment. As water demands increase, not only must large quantities of fresh water be made available, but natural water sources are being relied upon to dilute the polluted water discharged, compounding further the limited availability of freshwater. In many parts of the world, there is a widespread scarcity, gradual destruction, and increased pollution of freshwater resources. In the developing world, one person in three lacks safe drinking water and sanitation: the basic requirement for health and dignity