Water covers 70.9% of the Earth’s surface, and is vital for all known forms of life. On Earth, 96.5% of the planet’s water is found in oceans, 1.7% in groundwater, 1.7% in glaciers and the ice caps of Antarctica and Greenland, a small fraction in other large water bodies, and 0.001% in the air as vapor, clouds (formed of solid and liquid water particles suspended in air), and precipitation. Only 2.5% of the Earth’s water is freshwater, and 98.8% of that water is in ice and groundwater. Less than 0.3% of all freshwater is in rivers, lakes, and the atmosphere, and an even smaller amount of the Earth’s freshwater (0.003%) is contained within biological bodies and manufactured products. Water on Earth moves continually through the

hydrological cycle of evaporation and transpiration (evapotranspiration), condensation, precipitation, and runoff, usually reaching the sea. Evaporation and transpiration contribute to the precipitation over land. Safe drinking water is essential to humans and other life forms. Access to safe drinking water has improved over the last decades in almost every part of the world, but approximately one billion people still lack access to safe water and over 2.5 billion lack access to adequate sanitation.

There is a clear correlation between access to safe water and GDP per capital. However, some observers have estimated that by 2025 more than half of the world population will be facing water-based vulnerability. A recent report (November 2009) suggests that by 2030, in some developing regions of the world, water demand will exceed supply by 50%.

Water plays an important role in the world economy, as it functions as a solvent for a wide variety of chemical substances and facilitates industrial cooling and transportation. Approximately 70% of the fresh water used by humans goes to agriculture. Picturing water as a liquid that can form two types of structure, one tetrahedral and the other disordered, could explain many of its unusual properties.

Heating reduces the number of ordered, tetrahedral structures in favor of a more disordered arrangement in which molecules are more densely packed. . Water has an exceptionally high specific heat capacity. it takes a lot of heat energy to raise water’s temperature by a given amount.

Specific heat capacity is at a minimum at 35 °C but increases as the temperature falls or rises, whereas the heat capacity of most other liquids rises continuously with temperature. Water’s compressibility drops with increasing temperature until it reaches a minimum at 46 °C, whereas in most liquids, the compressibility rises continuously with temperature. .

Water molecules diffuse more easily, not less easily, at higher pressures. Unlike many liquids, water becomes less viscous, not more viscous, at higher pressures. . Properties such as viscosity, boiling point and melting point are significantly different in “heavy” water – made from the heavier hydrogen isotopes. .The thermal conductivity of ice falls with increasing pressure….all these things focus to a point “WATER IS PRECIOUS”…………………