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48
be treated also for the removal of color, taste, and odor. Coagulation is
commonly effected by adding to the water a salt of aluminum (usually
aluminum sulphate) or ferric iron. A precipitate forms and causes a clumping of
the bacteria and other foreign particles which then settle out during the several
hours of sedimentation; in this way 85% or more of the bacteria and suspended
particles can be removed. Activated carbon is sometimes added before
sedimentation to remove tastes and odors. In the process of filtration the water
is allowed to pass through layers of fine sand to remove remaining germs and
particles. Chlorine is commonly used to destroy harmful bacteria persisting in a
municipal water supply after the other treatments? Chlorine dioxide has more
recently been found effective as a destroyer of bacteria as well as means of
removing unwanted tastes and odors. Other means of destroying germs include
the use of ozone and of ultraviolet light. Some water supplies are aerated, i.e.,
exposed to the action of air and sunlight either through sprays or by running
over coarse gravel; taste and odor are improved and some germs are destroyed.
TEXT C. WATER SUPPLY.
Water is an important part of nature which surrounds us and of those
natural conditions we are changing constantly and ever more intensively: the
flora, the soil, the mountains, mineral resources, the deserts, the marshes, the
steppes and the taiga.
Water passes through a very interesting natural cycle. The atmosphere
which surrounds the earth’s surface contains water which varies in amount in
direct proportion to the temperature of its gases.. Water is also evaporated into
atmosphere. Atmosphere which has become saturated with water precipitates its
moisture when the temperature lowers. This phenomenon is termed rainfall.
The moisture falls to the earth and finds its way into a number of reservoirs
provided by nature.
Vast depressions in the earth are filled with water through the medium of
natural water sources such as rivers, lakes, etc. over the earth’s surface. These
bodies of water are classified as inland lakes and are excellent sources of water.
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