Types of Water Pollution
Water pollution can be divided into following categories depending on the source and storage of water:
(i) Groundwaterpollution
(ii) Surfacewaterpollution
(iii) Seawaterpollution
6.3.1 Ground Water Pollution
Water is considered to be a gift of nature.
Over 98% of the fresh water on the earth lies underground in the form of ground water (see sec. 5.2.1). It is the main source of drinking water for about 50% of the population on the global scale.Ground water gets polluted due to human activities (eg. industrial, domestic and agricultural activities). Generally, ground water contamination is irreversible. This lead to the degradation of water quality, i.e. objectionable taste, odour and excessive hardness) Following table gives the sources of water pollution along with the pollutants incorporated in water.
Table 6.1 Sources of contamination of ground water
| Sources of contamination | Contaminants discharged into ground water |
| Domestic wastes | Pathogenic organisms, nutrients and solids from domestic waste |
| Industrial wastes | Toxic heavy metals along with hazardous organic and inorganic effluents |
| Agricultural wastes | Fertilisers, pesticides, insecticides, herbicides. Leaches from agricultural land containing nitrates, phosphates and potash pollute the ground water |
Note: Ground water can also be polluted by septic tanks, refuse dumps.
The average chemical composition of ground water is given in Table 6.2. For comparison, the chemical composition of surface water (river) and sea water is also given.
Table 6.2 Chemical composition of ground water, river water and sea water
| Parameters (ppm) | Ground water (well) | Surface water (river) | Sea water |
| Chloride | 9.6 | 13 | 19 x 103 |
| Bicarbonate | 330 | 110 | 140 |
| Calcium | 92 | 36 | 400 |
| Magnesium | 34 | 8.0 | 1.35 x 103 |
| Iron(IΠ) | 0.09 | 0.02 | 0.01 |
| Nitrate | 13 | 0.1 | — |
| Potassium | 1.4 | 1.2 | 380 |
| Silica | 10 | 1.2 | 6.0 |
| Sulphate | 84 | 22 | 2.65 x 103 |
| Sodium | 8.2 | 6.5 | 10.5 x 103 |
| Total dissolved solid | 434 | 1.65 | — |
Harmful Effects of Ground Water pollution
Polluted ground water is a major cause for the outbreak of epidemics and chronic diseases like typhoid, jaundice, dysentery, diarrhoea, tuberculosis and hepatitis.
The use of polluted ground water for irrigatiιig damages the crops and decrease the yield of agricultural products. Polluted ground water affects fertility by killing bacteria and soil micro-organisms. A typical case of ground water pollution was reported on Sept 18,1988 by the ‘Hindu’ Newspaper. It reported the contamination of ground water in Medak district of Andhra Pradesh in India from different chemical industries which released poisonous chemicals. The ground water become greenish in color and emitted foul smell. It caused dysentery, vomiting, jaundice and diarrhoea and a number of deaths were reported. Some other harmful effects will form the subject matter of subsequent sections.In view of the above it is extremely necessary to protect ground water from getting polluted. This can be achieved by taking appropriate steps for predisposal treatment of toxic industrial effluents and municipal discharges. Also, location of wells for drinking water supplies should be very carefully decided.
6.3.2 Surface Water Pollution
Surface water in the form of rivers, streams and lakes is present to the extent of only 0.0091 percent of the total global water (see sec. 5.2). AU segments of our society (urban, rural, industrial, agricultural) are responsible for surface water pollution. Various processes and materials may pollute fresh water bodies. Some sources of surface water pollution are given in Table 6.3 below:
Table 6.3 Sources of surface water pollution
| Sources of contamination | Contaminants discharged into ground water |
| Agricultural run offs | Agrochemicals (pesticides, herbicides, fungicides) |
| Accidental spill of chemicals | Different chemicals |
| Leaks from surface, storage tanks or pipelines | Gasoline, oil |
| Run off from industrial sites like factories, refineries, mines etc. | Solvents, chemicals |
| Radioactive material processing plants | Radioactive materials |
The chemical composition of surface water (river water) is given in Table 6.2.
The maximum permissible limits of effluents discharged into surface water are given in Table 6.4 below:Table 6.4 Permissible Limits of Various Characteristics of Effluents
| Characteristics of effluents | Maximum permissible limit |
| pH | 5-9 |
| BOD | 20mg∕L |
| Suspended solids | 30mg∕L |
| Particulates | 15mg∕L |
| Cyananide | 0.1 ppm |
| Phenols | 0.5 ppm |
| Sulphate | 1 ppm |
| Toxic metals | 0.5 ppm |
Depending on the extent of pollution in surface water, it is harmful for life processes and sustenance of life. The harmful effects are similar to that of polluted ground water (see sec. 6.3.1). As far as possible, efforts should be made so that the surface water is free from following contaminants:
• Compounds imparting colour, odour, taste and turbidity eg. oils, greases, phenols, toxic materials.
• Substances which float on the surface as oil, scums etc.
• Toxic radionuclides
• Materials which are harmful for aquatic flora and fauna.
• Thermal effluents should not be discharged in the surface water.
• Chlorinated compounds
Lakes all over the world contribute to the surface water. The largest fresh water lake is Lake Superior in North America covering about 31,800 sq km. The deepest lake is Lake Baikal in Siberia, which is about 1940 m deep. Besides these, other well-known lakes are Dal and Nagin lakes in Kashmir and Nainital (India) and lake Michighan in USA. Due to pollution caused by various industrial, agricultural and chemical run off some of the lakes are in the process of dying.
6.3.3 Sea Water Pollution
Oceans are the major source of water in the world. Water bodies cover more than 70% of the earth’s surface. Due to population explosion and depletion of land resources, the food materials (e.g. fish etc.) are being used more and more. In this respect, human beings are responsible for destroying the aquatic environment either by mismanaging or by over exploitation. Oil pollution in the sea is the main factor which poses serious threat to the marine ecosystem and fisheries of the world. This aspect of marine pollution is discussed in chapter 7. Besides these, seawater is polluted by the discharge of various types of wastes from diverse human activities.
6.4