Water is an ionic solvent. Many dissolved salts may contain in water which is usually expressed as total dissolved salts (TDS). These salts include fluorides, nitrates and sulphates of many metals. Dissolved salts of calcium and magnesium are responsible for the hardness of water. The temporary hardness of water is due to the bicarbonates and permanent hardness is due to the chlorides and sulphates of calcium and magnesium. In some cases, salts hydrolyze resulting in hydroxyl ions. This will produce alkalinity in water. Oxygen is sparingly soluble in water and corresponding term is called dissolved oxygen DO. Do is accountable for aquatic life and oxidation of organic impurities in water. The industrial effluents contain a complex variety of substances. Their direct liberation into natural water causes water pollution and a decline in DO level. This is abridged by mechanical, physicochemical and biochemical methods.
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