We all know that sea water is salty. It contains many minerals which make it salty. Salinity of sea water varies a great deal in different parts of the ocean. On an average, there are 35 parts of salt to every 1000 parts of sea water. Now the question is whether it is possible to remove salt from the sea water and make it drinkable.
There are several methods to make the sea water drinkable. One method is distillation. In this, sea water is boiled and the steam is condensed into water. Water gets vaporized leaving behind the salt. Water so obtained is fresh and good for drinking. For this purpose, nuclear energy or solar energy is used.
In another method, electrical energy is used. Here, an electrical current is passed through the sea water. The electric current causes positive salt ions to flow in one direction and negative ions in the other. In fact, about 3.5 per cent of sea water consists of dissolved elements. These elements are sodium and chlorine which together form salt. On passing electricity, sodium ions move towards cathode and chlorine ions towards anode. This way, salt is removed from the water and water becomes worth drinking.
In another method, some special types of membranes are used to purify water. There are thin membranes which let pure water through while blocking the flow of salts. Water filtered with these membranes becomes pure.
By another method, the sea water is simply frozen. This process extracts salt from the water. After the salt has been separated from the ice, the ice is melted, giving fresh water. But this process is only for limited purposes.
One of the best methods of obtaining fresh water is called multi-stage flash distillation. In it sea water vaporizes rapidly several times, each time in a higher vacuum and at a lower temperature.
The world is now faced with an ever-increasing demand for fresh water.
Scientists in many countries of the world are developing new methods for obtaining fresh water from the sea. In Israel, for example, and other oil-producing countries in Middle East, it has become worthwhile to build big plants to distill fresh water from the sea. However, due to high cost in processing, it is not still considered economically viable as an alternate source of fresh water. The research on the subject is still in experimental stage.