Water Quality
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I-The hydrologic cycle (Water Cycle):
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II- Water Resources:a- Surface water
i. Fresh water (Rivers)
ii. Brackish water (Lakes)
iii. Saline water (Oceans & Seas)
b- Underground water (Wells &
Springs)
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Water pollution is the presence of any
material (contaminant) in water that is
harmful to human, animal and plant, or
affects its taste or odour.
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•Domestic water pollution
•Industrial water pollution
•Agricultural water pollution.
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The Quality of water is significant as its Quantity.
In fact, more than 97.5 % of earth’s water is saline,
and hence not readily available for use.
Water Quality is generally expressed in terms of
its Physical, Chemical and Bacteriological
characteristics.
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The change in chemical characteristics of
water alter water quality greatly.
For example, nitrites and nitrates in water
can cause methemoglobinemia, commonly
known as “blue baby syndrome”.
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Bacteria and microorganisms, present in water,
are of microscopic size (1 to 4 micron).
Harmful bacteria, causing different diseases, are
known as ‘pathogenic bacteria’, while the
harmless ones are known as ‘non-pathogenic
bacteria’.
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Note
The quality and composition of
dissolved salts in water depends upon
the nature of the rock or soil with
which it has come in contact.
Thus, ground water has generally a
higher salt content as compared to
surface water.
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General Standards of Quality of
Water for Different Uses
 The use of water may be grouped into:
i. Domestic
ii. Irrigational
iii. Industrial
Each group has its own standards of water quality.
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Domestic Use:
Water required for domestic purposes must
obviously be colourless, odourless and
tasteless.
It should be free from turbidity, chemical
compounds, harmful micro-organisms and
radioactivity.
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Standards for quality of water for domestic use
cannot be expressed in absolute values as they
vary with variations in human tolerance and
adaptability.
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For example, water having more than 500 ppm of
dissolved solids in not considered suitable for
drinking purposes in most of the humid temperate
regions of the world, whereas that with 1500 ppm
of dissolved salts is regarded as acceptable for
drinking in most of the arid regions.
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