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Pollution
Causes of water pollution
There are several classes of common water pol-
lutants. These are
disease-causing agents
(pathogens) which include bacteria, viruses, pro-
tozoa and parasitic worms that enter water from
domestic sewage and untreated human and
animal wastes. Human wastes contain concen-
trated populations of coliform bacteria such as
Escherichia coli and Streptococcus faecalis. These
bacteria normally grow in the large intestine of
humans where they are responsible for some
food digestion and for the production of vita-
min K. These bacteria are not harmful in low
numbers. Large amounts of human waste in
water, increases the number of these bacteria
which cause gastrointestinal diseases. Other
potentially harmful bacteria from human wastes
may also be present in smaller numbers. Thus
the greater the amount of wastes in the water
the greater are the chances of contracting dis-
eases from them.
Another category of water pollutants is
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