الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Water is a transparent and nearly colorless chemical substance that is the main constituent of Earth’s streams, lakes, and oceans, and the fluids of most living organisms. Pure water is tastless and colorless. Its chemical formula is H2O, meaning that its molecule consists of one oxygen and two hydrogen atoms, that are connected by covalent bonds [1]. Water is nonlinear molecule and strictly refers to the liquid state of that substance, that prevails at standard ambient temperature and pressure; but it often refers also to its solid state (ice) or its gaseous state (steam or water vapor). It also occurs in nature as snow, glaciers, ice packs and icebergs, clouds, fog, dew, aquifers, and atmospheric humidity. Water covers 71% of the earth’s surface and it is vital for all known forms of life. On Earth, 96.5% of the planet’s crust water is found in seas and 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 ice and liquid water suspended in air), and precipitation. Only 2.5% of this water is fresh water, and 98.8% of that water is in ice (excepting ice in clouds) 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. A greater quantity of water is found in the earth’s interior. Water on Earth moves continually through the water cycle of evaporation and transpiration (evapo transpiration), condensation, precipitation, and runoff, usually reaching the sea. Evaporation and transpiration contribute to the precipitation over land. Large amounts of water are also chemically combined or adsorbed in hydrated minerals [1].