The chemical composition of water bodies, e.g. ground water, surface water (river, lakes), oceans, etc., depends on their source.
Water is a gift of nature. Over 98 per cent of the fresh water on the earth lies below the earth as ground water. It is the main source of drinking water for about 50 per cent of the global population. It is generally believed that ground water is pure and safe to drink. However, this is not true. In fact ground water can easily be polluted from wastes generated from domestic, industrial and agricultural sources. The average composition of ground water is given in Figure
River Water and Lake Water:
River water and lake water are referred to as surface water. The rivers, as we know originate from the mountains and on way dissolve various minerals they come across. The lakes are formed mostly from river water. The river water originally is pure, but on its way it gets polluted from surface run off, industrial and municipal waste, agricultural wastes, decomposed plant and animal matter and radioactive materials. The average composition of surface water is given in Figure
The oceans have been used by man for centuries for recovering salt and other chemicals. In recent years, besides the chemicals, the oceans have become a good source of petroleum oil, natural gas, etc. The oceans get their water from various rivers. Since there is continuous evaporation from sea, the concentration of various constituents goes on increasing. The chemical composition of sea water is given in Figure
Besides the trace constituents given in the table, sea water contain about 25 other trace constituents in very minute amounts. These include Rb, Ba, Zn, Al, Mo, U, Ni, Mn, V, Ti, Co. Cd, Cr, Hg, Pb, F.
The composition of the ocean is generally expressed in terms of salinity. Salinity is defined as the total amount in grams of solid material dissolved in one kilogram of sea water, when all the carbonate has been converted to oxide, all the iodide and bromide have been replaced by chloride, and the organic matter has been completely oxidised. Salinity is expressed as gram of salt per kilogram of sea water (g kg 1), that is, as parts per thousand by weight (%). gives in the Figure : 4 below contribution to salinity of various inorganic salts. The salinity of all the oceans and seas is about 35 per cent. However small variations in salinity have been observed from place to place.