By far the most common substance on Earth is none other than water. Its usefulness is often taken for granted. Yet all forms of life depend on it and none can exist without it. Although water covers 70 percent of the Earth’s surface, most of it is salt water forming the great oceans.

It has often been said that water is life. This is so because animals, plant and all living things require a great deal of water. The human body consists of 65 percent water, a tree 50 percent and a non- woody plant 75 percent.

Water is made up of hydrogen and oxygen atoms. As a liquid, water has very useful properties. It freezes into solid ice at 0°C, turns itself into steam at 100°C and stays a liquid in between.

The water on the Earth’s surface is continually being recycled. It evaporates from the seas or oceans andcondenses into tiny droplets to form clouds that float in the sky. When clouds are too laden with moisture water, falls as rain, snow or hail.

On the ground, water flows into streams, rivers and lakes. Eventually it reaches the sea and the water -cycle starts all over again. Some of it, of course, sinksinto the ground where it is soaked up by the roots of plants. Underground water not tapped by roots finds its way into rock layers and remains there to form what is known as the water table.

Water is usually collected in reservoirs which may be formed by damming rivers or valleys. People need a lot of fresh water for many purposes. Domestic consumption includes drinking, washing, cleaning and watering plants. Industrial demand for water is heavy and vital for the manufacturing and treatment process.

Fresh water requirements are constantly on the increase. This drives scientists and engineers to explore new sources and to discover other ways of recycling water. Some water is obtained by pumping up from the underground rock layers. Other means include tapping the frozen water locked up in icebergs as well as seeding he clouds to induce rain. A method of getting fresh water is removing the salt from sea water. Such a process is known as desalination and it is widely used in the desert regions of the oil-rich Arab countries. However, it is quite costly to obtain fresh water by desalination and many countries just cannot afford the high costs involved.