OPTIONAL MODULE - 1 Chemistry
Environmental Chemistry
34
Notes
WATER POLLUTION
W ater is essential for the existence of all life forms. In addition to household uses,
water is vital for agriculture, industry, fishery and tourism etc. Increasing population,
urbanisation and industrialisation has led to the decreased availability of water. The quality
of water used is also being deteriorated as it is getting more and more polluted. You may
be aware of at least some health hazards and harmful effects of water pollution. In this
lesson a detailed account of various types, sources and effects of water pollutants is
given. Some methods of water pollution control and legislatures involved have also been
discussed.
Objectives
After reading this lesson, you will be able to:
list earth’s water resources;
define water pollution and its different parameters;
list the major types of water pollutants, their sources and effects;
distinguish between natural and man -made pollutants;
use the concept of biological oxygen demand (BOD) and account for the changes in
a water body;
state methods for the prevention of water pollution;
compare primary, secondary and tertiary treatment of sewage and
know necessary legislative measures for prevention of water pollution in the country.
34.1 Water Resources on Earth
You may be aware that about three fourths of our planet earth’s surface is covered by
water. However, very little of it is available for consumption. Most (about 97%) of the
water on earth is present in the seas and oceans. It is too salty to be of any use for
30
, Water Pollution OPTIONAL MODULE - 1
drinking, agriculture and industrial purposes. The remaining 3% is fresh water; 75% of Environmental Chemistry
which is locked up in the polar ice caps and in glaciers and quite deep under the earth’s
surface as underground water. The fresh water, which we can use, comes to us from two
sources:
i) Surface water
ii) Ground water
Let us learn about these in detail. Notes
(i) Surface Water: Rain and snow are good natural resources of fresh water. It is estimated
that of all the precipitation (rain water and snow) that falls on the earth, about one-third is
absorbed by the plants and another one-third seeps down into the soil and the remaining
one third runs off the surface into streams and rivers. This part of precipitation, which
runs off to form streams, rivers and lakes, is called the surface water.
Precipitation (rain or snow) that runs-off into stream, rivers and lakes is called
surface water.
The small fraction of usable surface water is continuously replenished by means of the
hydrological cycle, Fig 33.1.
Sun
Clouds
Precipitation
on Land
Precipitation Snow
Evapotranspiration
on Oceans
Percolation
Water Table
Evaporation River
Ground
Water Flow
Ocean
Fig. 34.1: A schematical representation of Hydrological cycle
The hydrological cycle involves evaporation of water from oceans, rivers and other sources
to form clouds. The clouds on saturation with water vapours cause precipitation falling
back on earth’s surface. On surface, the water runs off to rivers and finally to oceans.
The water again evaporates and the cycle continues.
Surface water has a natural tendency to clean itself as it contains certain organisms that
break down pollutants into harmless substances.
(ii) Ground Water: The part of precipitation that seeps into the ground as a result of
gravity and fills the pores between soil particles and rocks under it is called ground
31
Environmental Chemistry
34
Notes
WATER POLLUTION
W ater is essential for the existence of all life forms. In addition to household uses,
water is vital for agriculture, industry, fishery and tourism etc. Increasing population,
urbanisation and industrialisation has led to the decreased availability of water. The quality
of water used is also being deteriorated as it is getting more and more polluted. You may
be aware of at least some health hazards and harmful effects of water pollution. In this
lesson a detailed account of various types, sources and effects of water pollutants is
given. Some methods of water pollution control and legislatures involved have also been
discussed.
Objectives
After reading this lesson, you will be able to:
list earth’s water resources;
define water pollution and its different parameters;
list the major types of water pollutants, their sources and effects;
distinguish between natural and man -made pollutants;
use the concept of biological oxygen demand (BOD) and account for the changes in
a water body;
state methods for the prevention of water pollution;
compare primary, secondary and tertiary treatment of sewage and
know necessary legislative measures for prevention of water pollution in the country.
34.1 Water Resources on Earth
You may be aware that about three fourths of our planet earth’s surface is covered by
water. However, very little of it is available for consumption. Most (about 97%) of the
water on earth is present in the seas and oceans. It is too salty to be of any use for
30
, Water Pollution OPTIONAL MODULE - 1
drinking, agriculture and industrial purposes. The remaining 3% is fresh water; 75% of Environmental Chemistry
which is locked up in the polar ice caps and in glaciers and quite deep under the earth’s
surface as underground water. The fresh water, which we can use, comes to us from two
sources:
i) Surface water
ii) Ground water
Let us learn about these in detail. Notes
(i) Surface Water: Rain and snow are good natural resources of fresh water. It is estimated
that of all the precipitation (rain water and snow) that falls on the earth, about one-third is
absorbed by the plants and another one-third seeps down into the soil and the remaining
one third runs off the surface into streams and rivers. This part of precipitation, which
runs off to form streams, rivers and lakes, is called the surface water.
Precipitation (rain or snow) that runs-off into stream, rivers and lakes is called
surface water.
The small fraction of usable surface water is continuously replenished by means of the
hydrological cycle, Fig 33.1.
Sun
Clouds
Precipitation
on Land
Precipitation Snow
Evapotranspiration
on Oceans
Percolation
Water Table
Evaporation River
Ground
Water Flow
Ocean
Fig. 34.1: A schematical representation of Hydrological cycle
The hydrological cycle involves evaporation of water from oceans, rivers and other sources
to form clouds. The clouds on saturation with water vapours cause precipitation falling
back on earth’s surface. On surface, the water runs off to rivers and finally to oceans.
The water again evaporates and the cycle continues.
Surface water has a natural tendency to clean itself as it contains certain organisms that
break down pollutants into harmless substances.
(ii) Ground Water: The part of precipitation that seeps into the ground as a result of
gravity and fills the pores between soil particles and rocks under it is called ground
31
