The suitability of a water for a use depends on the type and amounts of some specific impurities present that will in some way affect the desired use. The various impurities present in a water are expressed through pollution parameters (water quality variables) broadly classified into three categories--physical, chemical and biological. The physical variables include general appearance, temperature, turbidity, colour, taste, odour, etc. Chemical variables include all possible inorganic and organic substances, such as pH, acidity, alkalinity, hardness, conduc- tivity, chlorides, sulphates, nitrates, nitrites, boron, heavy metals, pesticides, detergents, phenol, cyanide, radioactivity, 'bil, organics, Biochemical Oxygen Demand (BOD), Dissolved Oxygen (DO), etc. The biological variables include coliform MPN, Total Plate Count (TPC), bioassay counts or species diversity, etc.
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