definition 112 causes, effects and control measures of

Area Category

SPM µg/m3

SO2 µg/m3

Co µg/m3

NOx µg/m3

Industrial and mixed use

500

120

5000

120

Residential and rural

200

80

2000

80

Sensitive

100

3

1000

30

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Environmental Studies for Undergraduate Courses

our gardens. Like good health we ignore water

when we have it.

Although 71% of the earth’s surface is covered

by water only a tiny fraction of this water is avail-

able to us as fresh water. About 97% of the

total water available on earth is found in oceans

and is too salty for drinking or irrigation. The

remaining 3% is fresh water. Of this 2.997% is

locked in ice caps or glaciers. Thus only 0.003%

of the earth’ total volume of water is easily avail-

able to us as soil moisture, groundwater, water

vapour and water in lakes, streams, rivers and

wetlands.

In short if the world’s water supply were only

100 litres our usable supply of fresh water would

be only about 0.003 litres (one-half teaspoon).

This makes water a very precious resource. The

future wars in our world may well be fought

over water. By the middle of this century, al-

most twice as many people will be trying to share

the same amount of fresh water the earth has

today. As freshwater becomes more scarce ac-

cess to water resources will be a major factor in

determining the economic growth of several

countries around the world.