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.