The level of fresh water on the earth is decreasing every day. The availability of drinking water on the earth is limited while it is also getting polluted due to wrong activities of humans. In the absence of fresh drinking water it is very difficult to estimate the possibility of life on earth. Water pollution is the mixing of external elements through organic, inorganic, biological and radiological degradation of water utility and quality.
Hazardous pollutants carry various types of impurities including harmful chemicals, dissolved gases, suspended substances, dissolved minerals and germs. All pollutants reduce the amount of oxygen dissolved in water and affect humans and animals on a large scale. Oxygen present in water is dissolved oxygen required by aquatic system to continue the life of plants and animals. However, the oxygen required by the aerobic microorganism to oxidize organic material wastes is biochemical oxygen. Water pollution occurs due to two reasons, one is natural pollution (from rock deposition, organic matter weathering, dead organisms weathering, sedimentation, soil erosion etc.) and human-caused water pollution (forest cutting, setting up industries near aquatic sources, High level emissions of industrial waste, domestic sewage, synthetic chemicals, radioactive waste, fertilizers, pesticides etc.