Water pollution can be classified according to type of pollutants and on the basis of sources of pollution
i) On the basis of type of pollutants
a) Physical pollution is due to change in physical properties like colour, turbidity, taste, odour etc. of water.
b) Chemical pollution occurs due to change in chemical properties in presence of toxic inorganic and organic chemical pollutants.
c) Biological pollution is due to the presence of pathogenic bacteria, certain fungi, pathogenic protozoa, viruses and parasitic worms
d) Physiological pollution is due to presence of several chemicals such as chlorine, S02, H2S, ketones, phenols, amines etc. that changes physico-chemical properties of water.
ii) On the basis of sources of water
a) Ground water pollution (various pollutants are domestic waste, industrial waste, agricultural waste, runoff from urban areas, soluble effluents etc.).
b) Surface water pollution (caused by atmospheric gases, surface runoff, agricultural, industrial and municipal waste).
c) Lake water pollution (pollutants include surface runoff, discharge of organic waste, industrial waste, domestic waste etc.).
d) River water pollution (mainly due to the presence of atmospheric gases, industrial effluents, municipal wastes, decomposition of animal and vegetative material, weathering of soil and rock minerals etc. in river water).
e) Sea water (Marine) pollution (presence of oily waste, radioactive waste, industrial effluents etc. make sea water polluted).
Impacts of water pollution
A) On human health
A large number of dissolved pollutants (inorganic and organic) affect human health adversely leading to various diseases.
B) On plant health
Water Pollution that affects plants would include acid rain. Sulfuric and nitric acid rain washes nutrients out of the soil, damages the bark and leaves of trees and harms the fine root hairs of many plants which are needed to absorb water.
Since the acid concentration increases near the base of clouds by density, high altitude trees and vegetation may be exposed to pH levels as low as 3. At such acidic pH, plants absorb heavy metals and various nutrients from soil which can be injurious to plant health.
C) On Ecosystem
Biological oxygen demand (BOD)
Aerobic bacteria use oxygen dissolved in water by breaking down organic matter in the water.
The quantity of oxygen utilized by the microorganisms in aerobic degradation of organic matter in a water body is called BOD. Since BOD is proportional to the amount of organic matter present in water, it can be used as an indicator of the degree of water pollution. Unpolluted water show comparatively low values of BOD.
Eutrophication is the process of enrichment of water bodies by organic waste material containing nitrates and phosphates. Natural Eutrophication results from natural disintegration of rocks and mineralization of organic matter and is a very slow process. All nutrients fertilize algae and other water plants.
More of these plants grow as a result of additional nutrients. As a result more plant dies (excess of plants fight for space to grow). As algae dies, they add to wastes. Both the processes (growth and excess of waste utilization by plants) require oxygen.
This will in turn affect aquatic life (fishes). Thus, the water body smells offensively (since BOD rises). Eutrophication leads to growth of aquatic plants and algal bloom and ultimately water body disappear.
Xenobiotic compounds like heavy metal compound and polychlorinated biphenyls (PCBs) are difficult to metabolise, since they are non-biodegradable, stored in the body when enter into a biological tissue. This phenomenon is called bioaccumulation.
These toxic substances can enter to the biological food chain. Thus, enhancement in the concentration of various toxic substances along the food chain is called biomagnification.
Water Borne Infections
Water borne diseases are problems of immense proportion in India and other less developed countries. Eighty percent of the diseases in these countries are linked with contaminated water.
The microorganisms of diseases enter into the body through the drinking polluted water and multiply in the body of the infected person. The infection is excreted with the stool or urine and therefore, improper disposal of human excreta is the chief cause of contamination of water of rivers, lakes, hand pumps and results in the spreading of these diseases.
Among the water related diseases, polio, typhoid (viral), cholera, dysentery (bacterial) and dysentery (amoebic), diarrhoea, guinea worm, Japans encephalitis, malaria and Filariasis are common jaundice in our country.