Following are the sources of impurities in water:
a) Gases (O2, CO2 etc.) are picked up from the atmosphere by rainwater.
b) Decomposition of plants and animals remains introduce organic impurities in water.
c) Water dissolves impurities when it comes in contact with ground, soil or rocks.
d) Impurities are also introduced in water when it comes in contact with sewage or industrial waste.
Ground and surface waters can be contaminated by several sources which comprise of water from sewage, industrial and trade waste, agricultural run offs, sewage leakage, Physical pollutants and microbial pathogens.
Rain water: Chemicals released by smokestacks (chimneys) can enter the atmosphere and then fall back to earth as rain, entering seas, rivers, and lakes and causing water pollution. That's called atmospheric deposition.
The natural impurities which are collected from the atmosphere, catchment area and the soil are not essentially dangerous. These comprise of dissolved gases, minerals and suspended impurities and microscopic organisms.
The most serious kind of the water pollution is caused by human activity which is a result of Urbanisation and industrialisation.
The sources of pollution resulting from these are
a) Sewage: Domestic Sewage causes Ecological risks and health risks.
- Sewage originating primarily from kitchen, bathroom, and laundry sources.
- Waste from food preparation, dishwashing, garbage-grinding, toilets, baths, showers, and sinks.
This contains decomposable organic matter and pathogenic agents.
b) Industrial and Trade wastes: which contain toxic agents ranging from metal salts to complex organic chemicals.
1) It includes waste water from food processing industries and contains high concentrations of dissolved organic matter and may be highly alkaline from the use of lye.
2) Oil is mixed with water in the refining process of petroleum to remove salts and other impurities.
3) The use of bisulphite and sulphurous acid or sulphur dioxide in the paper manufacturing and pulping process yields waste sulphite liquor containing various wood by-products. There is presently a concern over the release of dioxins into waterways by the pulp and paper industry.
4) Agricultural pollutants: Run-off from crops contains pesticides, fertilizer, and sediment. Run-off from animal production facilities contains bacteria, organic matter, nitrates, and phosphates.
5) Physical pollutants: These include Dumping solid wastes and littering by humans in rivers, lakes and oceans. Littering items include cardboard, Styrofoam, aluminium, plastic and glass.
6) Radioactive substances may enter the water sources from the waste waters of nuclear power plants.
Contamination can arise in raw water as a consequence of improper storage or water may pick-up contaminants during supply from distribution systems. It can also occur as a consequence of leakage from a dirty water system into a clean water system.
Sewage and not the industrial pollution accounts for more than 75 per cent of the surface water contamination in India. Due to negligence, groundwater is also increasingly getting contaminated. In India less than 50% of the urban population has access to sewage disposal system. Most of the existing collecting systems are discharged directly to the rivers and other drinking water bodies without treatment. Garbage, domestic wastes are directly dumped into water bodies or roadside, which can often be washed into streams and lakes.
Bacteria, viruses and parasites can enter drinking water in many ways, for example as a result of animals excreting into a catchment area, from seepage of contaminated water into ‘leaky’ pipes in a distribution system, and from unhygienic handling of stored household water.
