b. Chemical Quality.
(1) Total dissolved solids . The TDS of water is composed of small amounts
of inorganic and organic substances or particles and mineral salts. The amount of each
substance is proportional to the amount of time the water has been in contact with
weathered rock, minerals, and other solids. The impure water may contain sulfate,
magnesium, chloride, iron, manganese, and other ions as shown in Table 1-2. The
TDS water quality standard is to prevent soldiers from getting chemically induced
diarrhea.
(2) pH value. The pH value measures the acidity or alkalinity of water. The
pH value midpoint is seven, which indicates a neutral solution. If acid substances in the
water predominate, the pH falls between 0 and 7. If alkaline substances predominate,
the pH is between 7 and 14. A value of seven does not necessarily mean that the water
is pure, since acids and bases in solution neutralize one another. The pH value of
water helps to determine the corrosiveness of the water, the amount of chemicals
needed to disinfect the water, and the ability of the analyst to determine if contaminants
are present. The various impurities in water, some of which are acids and some of
which are bases, increase or decrease respectively, the hydrogen ion activity in the
water. For a long-term (7 or more days) water source, the pH standard of water is
between 5.0 to 9.2 units.
(3)
(a) Oxygen. Rainwater contains large amounts of dissolved oxygen as
does surface water where fish are plentiful. However, the amounts in surface water
vary, as does its concentration of dissolved oxygen. Oxygen can, especially when
carbon dioxide is also present, cause many metals to corrode. Therefore, use less
oxygenated water for parts such as vehicular radiators
(b) Carbon dioxide. The atmosphere, decomposing vegetation, and
underground sources cause carbon dioxide (CO2) to enter water. When this happens,
carbonic acid is formed. Carbonic acid aids in the formation of bicarbonates of calcium
and magnesium.
(c) Hydrogen sulfide. Hydrogen sulfide (H2S) is produced by the
decomposition of organic matter and by the breakdown of certain compounds
containing sulphur. It gives off an odor of rotten eggs and most likely is composed of
large amounts of industrial or animal wastes. This gas is corrosive to metals. In small
amounts, it is unpleasant; in large amount, it is also harmful.
and should be avoided. Current water treatment methods are able to ensure that water
is potable. The water quality standard is 1000 pc/L for gross beta activity and 10 pc/L
for strontium 90.
MD0160
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