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Pick
up a glass of water, and hold it to the light. Can you
see any finely divided, insoluble particles suspended in
water? Or does the water seem hazy? If so, the water is
turbid.
When
water has a large amount of such suspended particles, we
lose our zest for it. While it may be safe to drink, it
seems offensive.
The
U.S. Public Health Service Drinking Water Standards
recommends that turbidity of potable water be less than
5 units.
The
suspended particles clouding the water may be due to
such inorganic substances as clay, rock flour, silt,
calcium carbonate, silica, iron, manganese, sulfur or
industrial wastes
Again
the clouding may be caused by organic substances such as
various microorganisms, finely divided vegetable or
animal matter, grease, fat, oil and others.
While
turbidity may be due to a single foreign substance in
water, chances are it is probably due to a mixture of
several or many substances.
Those
particles which quickly sink to the bottom are usually
called sediment. There are, however, no hard and fast
rules for classifying such impurities.
If
you take water from a swiftly flowing river or stream,
you generally find that it contains a considerable
amount of sediment.
In
contrast you find that water taken from a lake or pond
is usually much clearer. In these more quiet, nonflowing
waters there is greater opportunity for settling action.
This all but very fine particles sink to the bottom.
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