definition 112 causes, effects and control measures of

non-point sources

 of

pollution.

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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