Like clean air, fresh water is also becoming a scarcity. The limited availability of fresh water and its unequal distribution make water pollution a matter of great concern. Water pollution is generally localized and confined, making it more severe.The pollutants undergo many reactions and can become hazardous. 70 % of India’s fresh water is polluted, including several high altitude lakes. While water pollution is easier to study and manage, its control is highly complex and very costly.Water pollution is defined as presence of any foreign substance (organic, inorganic, biological or radiological) in water which tends to degrade the quality so as to constitute a hazard, or impair the usefulness of water.It contains various types of impurities such as dissolved gases, dissolved minerals, suspended matters and even microbes. The presence of water pollutants alters the amount of dissolved oxygen and biochemical oxygen demand.Dissolved oxygen (DO) is the amount of oxygen present in the aquatic system that is available for aquatic life and is essential for sustaining the plant and animal life in any aquatic system. The Biochemical Oxygen Demand (BOD) is a measure of the oxygen required by aerobic micro-organisms to bio-chemically oxidize the organic matter present in the waste and is expressed in mg/1.Another quick measure of organic matter present in waste is Chemical Oxygen Demand (COD) and in this case chemical oxidants (potassium dichromate in acidic conditions) are used instand of aerobic micro-organisms for the oxidation of organic matter. Generally COD of a waste will be higher than its BOD because more organic compound can be chemically oxidized than bio­chemically.
Types of Water Pollution:Natural Water Pollution:Leaching of rocks, decaying of organic or dead matter, soil erosion and silting etc.Man-made Water Pollution:Deforestation, industrial set up near water bodies, industrial waste, domestic sewage radio-active waste, synthetic chemicals, fertilizers and pesticides etc.
Water pollution is one of the most serious environmental problems. It occurs when water is contaminated by such substances as human and animal wastes, toxic industrial chemicals, agricultural residues, oil and heat. Most of our water bodies— rivers, lakes, seas, oceans, estuaries and underground water sources are gradually becoming polluted. In the course "Covered so far, you have seen how deforestation, urbanization, intensive agriculture and industrialization have caused pollution of water bodies. You are familiar with various aspects of air pollution, including harmful effects of acid rain. In this unit we will summaries various types of water pollution caused by different pollution sources, and also explain some important concepts such as point and non-point sources, biological oxygen demand self-purification capacity of natural waters, infiltration of pollutants to groundwater, thermal pollution and pollution caused by accidents in oil tanker ships(oil spills). In the next unit you will read about the degradation of land resources and terrestrial features of earth. Polluted water may look clean or dirty, but it invariably contains germs, chemicals or other materials that can cause inconvenience, illness or death.