Disease – causing agents (Pathogens): When a source of pollution can be readily identified because it has a definite source and place where it enters the water it is said to come from a point source. It refers to contaminants that enter a water way through a discreet conveyance, such as pipe or ditch. E.g. municipal and industrial discharge pipes; pollutants are organics or metals
Oxygen depleting wastes: Many wastes can be decomposed by aerobic bacteria. Large pollution of bacteria use up oxygen present in water to degrade these wastes. The amount of oxygen required to breakdown a certain amount of organic matter is called biological oxygen demand (BOD). The amount of BOD in the water is an indicator of the level of pollution. Too much of organic matter in the water uses up all the available oxygen and due to this all the oxygen dependent aquatic life would die. Due to which the anaerobic bacteria breaks down the wastes and produces a foul odour and unpleasant taste.
Inorganic plant nutrients: These are water soluble nitrates and phosphates which cause the excessive growth of algae and other aquatic plants. Excessive growth due to added nutrients is called ”Eutrophication”. Eutrophication interferes with the use of water by clogging up water intake pipes which changes the taste and odour. As the organic matter decays, oxygen levels decrease and fish and other aquatic species die.
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