Water covers two-thirds of the Earth’s surface, with over 97% present in the oceans and less than 1% in freshwater streams and lakes.

1. WATER POLLUTION
Water covers two-thirds of the Earth’s surface, with over 97% present in the oceans and less
than 1% in freshwater streams and lakes. Water is also present in the atmosphere in solid
form in the polar icecaps and as groundwater in aquifers (water-bearing rocks) deep
underground. Water has many remarkable properties. It is sometimes referred to as ‘the
universal solvent’, readily dissolving a wide range of chemical substances. It also acts as a
fluid medium facilitating the dispersal of un-dissolved particulate matter.
Water pollution may be defined as any chemical or physical change in water
detrimental to living organisms. It can occur through natural processes, for example by
sediments produced by natural erosion. Water bodies are a major recipient of an extensive
array of wastes produced by human activity. These may be discharged directly into
watercourses by sewers or pipes from factories or be washed down from agricultural or urban
areas particularly after heavy rains. Under rather exceptional circumstances, water bodies
may become significantly contaminated by the atmospheric deposition of pollutants.
Water pollution is a global problem and one that does not respect national boundaries.
Sources of pollution may be domestic, agricultural or industrial. In less-developed countries,
human and animal waste and sediments from unsound agricultural and forestry practices are
the main pollutants. In more-developed countries; industrial pollutants, such as toxic metals,
organic Chemicals and heat add to the water pollution problem. The effectiveness of treating
wastes prior to their release into the environment determines the balance between potential
and actual pollution.
The release of large quantities of oxygen-demanding organic waste into watercourses
often has disastrous effects on the indigenous flora and fauna. The primary source of organic
waste released into fresh waters is sewage effluent. Other sources include run-off from urban
areas and farms, and some industrial effluents. The recent intensification of livestock
production, with larger herds concentrated in smaller areas, has exacerbated the problem of
organic pollution from farm animal wastes.
Aquatic primary productivity is often limited by the availability of inorganic plant
nutrients. In freshwater lakes and rivers, the limiting nutrient element is usually phosphorus,

2. whilst in marine waters nitrogen is often in short supply. If small amounts of nutrients enter
aquatic ecosystems where they are normally limiting, primary productivity is stimulated. The
water body becomes over-enriched by excessive nutrient input and consequently polluted.
Both acid rain and acid mine drainage contribute significantly to the acidification of
natural waters. These two phenomena are dealt with in detail in this section. However, there
are other causes of this particular type of water pollution. For example, the planting of
extensive tracts of coniferous forests, usually in upland areas, results in the acidification of
the soil and the waters which drain these plantations.
Organochlorines are, as name suggests, organic compounds containing chlorine.
Manufactured organochlorines include a number of pesticides, for example DDT, and
polychlorinated biphenyls, or PCBs as they are known. These two groups will be considered
separately, although they do share a number of important characteristics. For example, both
groups are reported to have endocrine-disrupting properties.
Drilling for oils is one of the major extractive industries. Crude oil is a complex
mixture of thousands of different organic molecules, mainly hydrocarbons (aromatics,
alkenes and cyclohexanes). It is refined by the process of fractional distillation to yield a
number of commercially important products such as petrol, diesel oil and tar. From these
different types of oil, seas and rivers are being polluted regularly. Sometime accidental
spillage from oil tankers causes drastic damage to the environment through oil pollution. All
types of aquatic forms of life thus face the ill-effects.
Water is able to absorb large quantities of heat without appreciably increasing its own
temperature or changing from its liquid sate. This high heat capacity means that it is
extensively used as a coolant in many industries. The principal user of water as a coolant is
the electricity generating industry. They often discharge a huge quantity of hot water and thus
causing thermal pollution.

3. Thermal pollution affects aquatic ecosystems in a variety of ways. In general, the
species composition changes as species tolerant of warmer waters replace those unable to
adapt. This transition is often accompanied by an overall decrease in species richness. For
example, attached algae in heated effluents were reported to show an increase in biomass but
a decrease in the number of species represented.
Fluoride and Arsenic pollutants are important amongst the inorganic pollutants. Vast
areas of Haryana, Rajasthan and Punjab are highly contaminated with fluoride compounds in
potable water. There the amount of fluoride present in water is very high above the danger
level. Flow of waste products from glass industry, hydrocarbon producing industry etc.
carrying high amounts of fluoride compounds, polluted water bodies there.
Water gets polluted when underground layers of Arsenic come in contact with ground
water. Ground water from the tube-wells is highly contaminated with arsenic compounds in
six districts of West Bengal covering a vast area. Here the amount of Arsenic compound is as
much as 200 times higher than its permissible amount. Apart from West Bengal, the long and
vast Gangetic basin of India including Bihar, Jharkhand and some part of Uttar Pradesh is
highly contaminated with arsenic compounds. Even in Bangladesh the ground water is highly
polluted with arsenic compounds. Symptoms of arsenic pollution are ‘melanosis’ where large
black spots appear all over the body surface. Tumors may appear in the feet and it’s sole.
Bronchitis, Cirrhosis of liver, skin cancer etc. is the other effects of Arsenic pollution.
There are Various preventive measures can be taken to combat water pollution such
as Underground water can be saved from pollution if the land is not exposed to harmful
pesticides and other industrial chemicals. The farmers should be encouraged for organic
farming. Industries should not be allowed to discharge untreated chemicals into the water
bodies. There should be a mechanism to ensure that only harmless substances are poured into
rivers, lakes and oceans. The domestic sewage system should be designed in a scientific
manner.