Almost seventy percent of the surface of the Earth is covered by water bodies and as much as 97 % of it is found in the oceans. There has always been a dearth of fresh water supply and sea water purification has emerged as one of the ways to derive fresh water. Scientists from several parts of the world believe that desalinizing water from the oceans and seas may go a long way in resolving the water crisis.
Sea water though available in a large volume cannot be utilized for consumption or for agricultural and industrial purposes. The saline content proves to be detrimental to one's health. It causes dehydration of the body cells and also causes sufficient damage to crops as well. Over the years, scientists have come up with several methods of sea water purification. By installing the required instrument for this purpose and by executing the correct procedure, fresh water can easily be derived from sea water. These include electro dialysis, reverse osmosis and distillation.
Of all these methods, distillation is the most widely used method of reducing the salinity of water. It is cost effective and commercially viable too. The process of distillation is more or less based on the everyday phenomenon of evaporation. The heat emanating from the rays of the Sun causes water from the surface of oceans and seas to evaporate. The vapor thus formed gradually cools down owing to condensation and comes back on the surface of the earth as rain. This process has often been used to remove the saline content of the water. The process of solar distillation, in which a basin of water is covered by glass or transparent plastic and left beneath the sun, is seldom used. It involves a sizable expenditure. In the present context, distillation is carried out by the process of multistage flash distillation. It adheres to the conventional processes of boiling followed by condensation. The process yields crystal clear water and at times it is devoid of any taste. This process is used at a naval base at Guantanamo Bay in Cuba.
Another method that is used to desalinate water is known as reverse osmosis. In reverse osmosis water high on saline content is passed through a membrane. In this process while the salt is left behind, fresh water is easily obtained. This process of reverse osmosis for sea water purification is carried out at Cape Coral.
The third process of sea water purification is that of electro dialysis. Electro dialysis works on the principle that when salt is dissolved into water it gradually disintegrates into ions of chloride and sodium. The procedure is carried out in a chamber composed of clearly demarcated compartments. When electricity is passed the negatively charged chloride ions are drawn towards the positive electrode in the compartment. The positively charged sodium ions on the other hand move towards the negative electrode. This is how the salt is done away with while the fresh water remains as a residue.
The rise in the demand for fresh water has led the scientists to experiment and devise new methods of desalinating water. One of these is the process of freezing whereby the water from the seas is frozen and the ice crystals that are formed is pure water in a solidified form. The problems of carrying out such an elaborate process involve substantial expenditure. The plants, where the process of desalination is carried out, yield 31 billion gallons of fresh water. One such plant where sea water purification is carried out on a large scale is the Al Jubayl in Saudi Arabia. Sea water purification helps to generate water resources and thus meet the water requirements of the world.