The water problem

Water is the most common of all liquids and probably the most useful. Naturally occurring forms such as sea water, rain water and lake water are never pure. Consumption increases annually, millions of tons are used each day in industry, so in this respect there is no wonder that there is a water problem. The answer to heavy demands might well be the sea which covers most of the Earth's surface.

Sea water varies in composition, but is, in fact, a vast store house of substances apart from water. In the English Channel there is about 3.5 per cent of solids dissolved in the water, in the Red Sea about 4.1 per cent, while in the Baltic it can be as low as 0.5 per cent. Sodium chloride, common salt, is the most abundant of the solids present. From your knowledge of separation so far, you can easily understand that distillation of sea water would give pure water and leave the solids in the distillation vessel. Of course this has been realized for a lone, time but the difficulty has been in carrying out this operation economically. To satisfy the heavy demands of industry, a great deal of fuel would be needed to carry out the distillation. However, using the Sun as the source of heat, purification of sea water has successfully been carried out in some countries in recent years.