Water is extremely essential for life, this common fact is known to all. It is required to meet our basic needs in day to day life viz., cooking, drinking, bathing, disposal of sewage, irrigation, generating electricity in power plants, cooling and manufacturing different products in industries and the disposal of industrial wastes. During all these processes the undesirable substances are added to the water resources to a great extent. This alters the basic chemistry of water in rivers and streams.
Sources of Water Pollution
(i) Domestic sewage:
This includes household’s wastes like food wastes, synthetic detergents used for washing clothes and cleaning bathrooms and latrines and water-based paints.
(ii) Industrial effluents
The industrial wastes are discharged into the adjoining rivers and streams through flush lines of factories. The textiles, sugar and fertilizers factories, oil refineries, drugs manufacture, rubber, and rayon fibres, the paper industries and the chemical factories all produce Chemical pollution.
(iii) Agricultural source
Increased use of fertilizers has become essential for high yielding crop plants. Excess of nitrates used as fertilizers seep into groundwater is carried into lakes and pond. On entering the drinking water supply system these create several health problems.
These include insecticides, fungicides, nematicides, rodenticides, herbicides and soil fumigants. These contain chlorinated hydrocarbons, organophosphates, metallic salts, carbonates, acetic acid derivatives etc. many pesticides are non-degradable. They pass through the food chains and accumulate in fatty tissues thus causing several health hazards.
(v) Thermal pollution
Power plants and nuclear power stations are the main sources of thermal pollution of water where water is used for cooling and becomes hot. The hot water on entering the main water body raises its temperature, which kills fishes and other aquatic animals and increases the rate of respiration in aquatic plants.
(vi) Pathogenic organisms
Sewage and domestic waste from houses introduce pathogenic organisms viz., protozoa, worms-eggs and bacteria into the water. This contaminated water if consumed causes jaundice, typhoid, dysentery, cholera, tuberculosis etc.
(vii) Mineral oils
Oil from oil spills and washings of automobiles find way into river water through
(viii) Underground water pollution
Underground water, particularly in cities and industrial areas, is no more pure and safe. The sources of underground water pollution are sewage, seepage, pits, industrial effluents, septic tanks, fertilizers and pesticides, garbage etc.
(ix) Marine water pollution
River and stream network sources of water ultimately end up ocean and seas. Thus,
these acts as the sink of all natural and man-made water based pollutants. The main
sources of oceanic pollution are discharges of oil, greases, petroleum products, detergents, sewage and garbage including radioactive wastes.
Effect of Water Pollutants
The main effects of water pollutants are:
- Compounds of mercury, arsenic and lead are poisonous and chemically harmful as
they even affect water treatment plants e.g. organic sulphur compounds interfere
- Mercury, when dissolved in water, is absorbed by aquatic plants and enters the food chain. Lead impairs metabolism and brings about congenital deformities, anaemia etc.
- Cadmium damages kidneys and liver.
- Inorganic nitrates and phosphates promote the growth of oxygen-consuming algae,
which result in the death of fishes and other aquatic animals.
- Presence of dyes and compounds in the discharged water changes the colour of
- Soap, detergents and, alkalis result in foam formation.
- Industrial effluents containing iron, free chlorine, phenol, manganese, oils,
hydrocarbons, ammonia, algae and microorganisms impair the taste and odours of
- The nitrates and phosphates dissolved in water accelerate the growth of
microorganisms, which consume much of the dissolved oxygen depriving fish and
other aquatic life (Eutrophication).
- Biomagnifications is the increase of toxic materials at each trophic level of a food
For example, DDT after reaching a water system is absorbed by the microorganisms on
which smaller fishes feed. From them, DDT reaches the carnivorous animals. Since bigger fishes consume more food, large amounts of DDT accumulates in their body.
Control Of Water Pollution
- Separate ponds and tanks to be used for cattle and animals.
- Use of pesticides, insecticides and fertilizers should be done judiciously. Rapid biodegradable substitutes for pesticides should be employed.
- In towns where sewage facilities are not available, septic tanks should be made in
- Rivers and lakes should not be used for bathing or washing as it contaminates water.
- Domestic sewage and industrial wastes should be treated before discharging them into drains.
Treatment of Waste Water
Domestic sewage and industrial wastes should be properly treated before these are
drained in the mainstream water. Treatment involves the following two steps:
(i) Sewage treatment
It involves following steps:
Primary treatment. It involves physical processing of sedimentation, flotation and
filtration where sewage water is passed through screens to remove larger particles and then through grinding mechanism to reduce the larger particles to the smaller size. The sewage is finally passed through settling tanks to remove suspended impurities.
Secondary treatment. Sewage obtained after primary treatment is sent to aeration tank where it is mixed with air and sludge laden with bacteria and algae. The algae provide oxygen to the bacteria and decompose organic matter into simple compounds. Chlorination is finally done to remove bacteria.
Tertiary treatment. In the third and last step, water is passed through ion exchangers
to remove dissolved salts.
(ii) Treatment of industrial effluents
Treatment of industrial effluents involves neutralization of acids and bases, removal of toxic compounds, coagulation of colloidal impurities, precipitation of metallic compounds and reducing the temperature of effluents to decrease thermal pollution.