The harmful effects of water pollution can be divided into three groups, viz., (i) Effect on man, (ii) Effect on aquatic life, and (iii) Other effects.
1. Effects on Man:
On a worldwide scale, the pollution of water supplies is probably responsible for more human illness than any other environmental influence. The diseases so transmitted are chiefly caused by micro-organisms and parasites. Sewage and polluted water are responsible for several water-borne diseases.
Some of the diseases caused by polluted water are cholera, typhoid, infantile diarrhoea, dysentery, infectious hepatitis, polio, giardiasis, amoebic dysentery, jaundice, zondic, etc. Cholerais an illness caused by ingestion of the bacterium Vibriocholeral, results rapidly in massive fluid depletion and death in a very large percentage of patients.
It is transmitted by drinking water contaminated with the faces of infected individuals. In developing countries, deaths by cholera are still common. Guineaworm is another disease caused by polluted drinking water.
In India alone, about 18 lakh people suffer from this disease. Schistosomiasis is a group of diseases caused by infection through worms in water.
There are certain chemicals present in polluted water which may cause diseases like nepurities, wrist drop, foot drop, etc. In spite of drastic measures taken for the supply of purified drinking water in USA, there are incidents of diseases caused by water contamination in one way or other. The developing countries of Africa, Asia and Latin America, where arrangements of water treatment are limited or negligible, a large section of the population is susceptible to water-borne diseases.
2. Effects on Aquatic Life:
The effect of water pollution is more on aquatic life, because their existence depends on water and when there is any disturbance in their ecosystem, the impact is maximum on them. In polluted water, due to abundant growth of algae, the oxygen content becomes lesser, causing the death of fishes and other organisms. It is estimated that during the last twenty years, there is a decrease of about 40 per cent in aquatic life.
Algae are responsible for imparting a peculiar taste and odour to many of the water supplies and also are a cause of gastroenteritis. A report by Wheler indicates that algal poisons usually act on the central nervous system and skin and is reported to be capable of producing cirrhosis of the liver.
There are many cases on record of the destruction of marine life by polluted water. Mass killing of fish was among the earliest and most dramatic result of indiscriminate pollution of water. Another type of fish killer is pollution from municipal sewage. Industrial, thermal, radioactive pollution, etc., are also threats to marine life.
Because of water pollution large number of ducks also dies every year. For example, 1, 40,000 ducks died of botulism in California in 1970. Occasional deaths of animals have also been reported by drinking of polluted water. If water pollution is more severe, the process of photosynthesis is also obstructed which affects the growth of aquatic vegetation. All the chemicals that are drained into the water have harmful effects on every organism that survives there.
3. Other Effects:
Due to water pollution, the physical and physiological nature of water has also changed. The colour of water changes due to pollutants, mainly due to organic dyes. The colour in itself is not harmful; however, aesthetic considerations make coloured water unsuitable for any purpose.
The turbidity caused by the presence of colloidal or suspended matter is the characteristic trait of sewage and industrial effluents.
Generally, the more the turbidity, the stronger is the sewage or effluent and the effects are worse. Foam is the product of water mixed with soaps and detergents. It consists of a suspension of air bubbles in water medium.
Industrial effluents containing chemical substances, such as iron, chlorine, phenols, etc., affect the taste of the water. The decomposition of organic matter and algae, fungi and filamentous bacteria also imparts peculiar tastes. Similarly, the odour of water also changes due to the presence of pollutants.
Even small amount of sulfides because bad odour in water. The pollutants also reduce the transparency of water. Oil spills have their effect over evaporation. The industrial effluents, which contain several types of chemicals, are also responsible for the loss of soil fertility. In fact, the effects of water pollution are multidimensional in nature.
Apart from above mentioned direct effects, there are several indirect effects also. Thus, water pollution has become a threat to the ecosystem and an important cause of environmental degradation.