Water is never pure in nature except the rain water. It is always contaminated with various kinds of substances. These substances present in water, when exceed certain limit cause water pollution. The quality and quantity of these substances present, determine the nature and magnitude of pollution.

Nature and Magnitude of Water Pollution:

Polluted water shows certain characteristics. These characteristics determine its nature.

(a) Bad taste of drinking water.

(b) Offensive odors’ from lakes, rivers and ocean beaches.


(c) Unchecked growth of aquatic weeds in lakes .and ponds.

(d) Decreasing number of fishes and other aquatic animals in fresh and marine water.

(e) Oil and grease floating on the surface of the water.

Polluted water contains impurities of mainly two kinds.


(1) Dissolved impurities and

(2) Suspended impurities.

(1) Dissolved impurities:

Certain gases like carbon dioxide, ammonia, nitrogen and certain salts like nitrate, phosphate and sulphate and certain metals like calcium, magnesium, manganese, iron etc. remain in dissolved salt in water. Increase in the concentration of these substances lead to water pollution.

Water is also sometimes contaminated with certain heavy metals like; lead mercury, chromium, nickel and zinc etc. It is fatal if the concentrations of these substances in water exceed certain limit.


Farmers use in agriculture large quantities of fertilizers for increasing soil fertility and various kinds of organic compounds to kill insects, pests, fungi and herbs. These are collectively called pesticides. Common pesticides are D.D.T (Dicholoro Diphenyl Trichloro Ethane), malathion, parathion, 2-4-D (2-4-Dichlorophenoxy acetic acid) etc. Through rain water; these harmful chemicals enter into water bodies and cause severe pollution.

(2) Suspended impurities:

Some substances remain in suspended state in water. They are dust, sand, clay, silt and mud. The microscopic plants and animals are also present in suspended state in water. They are called planktons.

Both dissolved and suspended impurities are responsible for colour, odour and turbidity of water. When some pathogenic bacteria such as E.coli and other bacteria are present, they cause serious deseases like diarrhoea, jaundice, typhoid and other diseases related to alimentary canal, if that water is used for drinking purpose.

All these are natural impurities and are derived from the atmosphere, soil and rock. (Table – 9)


Impurities in Natural Water


Suspended Particles

Dissolved Particles


Dust Sculpture Dioxide

Carbon Dioxide, Nitrogen, Oxygen etc.

Minerals soil and rock

Sand, clays, minerals soil

Soleplate, Nitrate, Phosphate, chloride Sodium, fluoride, Calcium Magnesium, Iron

Living organisms and their deco, position product





Living organisms can tolerate unto certain concentrations of all these impurities. It is called “Tolerance limit”. If their concentrations are increased and crossed that limit, the result is “pollution of water” sometimes it is so serious that living organisms cannot grow and die.

Sources, of Water Pollution:

The substances including organic and inorganic matters, mineral salts, heavy metals, oil and greases that pollute the water are called the pollutants. The main sources from where water gets pollutants are:

(1) Sewage and other wastes.

(2) Industrial wastes containing toxic substances of metals, organic and inorganic in nature.

(3) Agriculture runs off wastes comprising fertilizer and pesticides.

(4) Physical pollutants i.e. heat (thermal pollution) and radioactive substances.

Both the surface and ground water is polluted by these unwanted waste materials.

(a) Surface water pollution:

(such as ponds, rivers, streams etc.) is mainly polluted by improper discharge of untreated municipal wastes containing sewages.

Sewage: Sewage is the used up water by a community i.e. the waste water and consists of: Domestic water borne wastes including human excrement and wash waters. Everything that are released to the municipal sewage system through the drains of homes constitutes the sewage.

(1) Industrial wastes, such as acids, greases and animal and vegetable matters discharged by factories.

Sewages, when relapsed to the surface water like lakes, rivers or ponds cause three things:

(i) It adds intestinal bacteria and other pathogenic organisms which can spread diseases like cholera, dysentery, typhoid and infectious hepatitis (jaundice.)

(ii) It adds toxic substances like mercury, nickel, cobalt etc. from industrial effluents to lake, river or sea.

(iii) It contributes organic matters which stimulate the growth of organisms that may use up the entire dissolved oxygen available in the water body. That leads to eutrophication. Fishes may die in acute absence of dissolved oxygen.

(b) Ground water pollution:

Ground water is the main source of drinking water for most of our rural villages. Sometimes underground water sources are also polluted. The main causes are seepage pits, refuse dumps, leakage from septic tanks, barnyard manures and industrial effluents like nickel, iron, copper, chromium or certain organic matters from various industries.