(a) Iron. Iron is undesirable because it imparts a rusty color and objectionable taste
to water. It also forms crusts in plumbing and piping. When iron is present in water, organisms whose
life processes depend on iron compounds may also be present. These organisms may cause tastes and
odors and create what is called "red water."
(b) Manganese. While not encountered as often as iron, it is found in both surface
and ground water. Its presence in water normally causes a gray or black color.
(c) Sodium carbonate and sodium bicarbonate. These increase the alkalinity of the
water, thus raising its pH value.
(d) Sodium chloride. Sodium chloride is of importance principally in connection
with the salty tastes produced and in identifying the nature of noncarbonate hardness.
(e) Sodium sulfate. This has a laxative effect when present in water in amounts over
500 PPM. In large amounts, it causes foaming in boilers and distillation units.
c. Dissolved Gases. The concentration of a gas in water is directly proportional to the
concentration, or partial pressure, of the gas in the atmosphere in contact with the water surface. In
general, this involves the water temperature, its salinity, and the altitude. The gases of primary interest
to water supply are listed as follows:
(1) Oxygen. Large amounts of dissolved oxygen are found in rainwater. The amounts in
surface water vary greatly, depending on the amount and type of pollution, the degree of self
purification, the action of algae, and the temperature of the water. Polluted water will exhaust the
oxygen supply, while clean water will contain much dissolved oxygen. Cold water contains larger
amounts of dissolved oxygen than warn; as water temperature rises, the dissolved oxygen is released to
the atmosphere. Decreased pressure on water has the same effect, releasing oxygen to the atmosphere.
Dissolved oxygen causes the solution of metals and, especially in the presence of carbon dioxide, causes
many metals to corrode.
(2) Carbon dioxide. The presence of carbon dioxide in water contributes to the degree of
hardness and acidity of the water. Water acquires this gas in several ways: from the air by the natural
movements of water in contact with the air, such as currents and wave action; by contact with
decomposing vegetation, which gives off carbon dioxide freely; and by contact with the gas in
underground deposits. High carbon dioxide content usually makes water more corrosive to metals.
(3) Hydrogen sulfide. Hydrogen sulfide in solution lends a disagreeable taste and
rottenegg odor to water. Ground water absorbs sulfides by passing over sulfur-bearing rocks. Water
purification teams frequently run into this condition when using the ocean intake system to draw water
during coastal operations. Hydrogen sulfide is also responsible for the destruction of cement and
concrete as well as the corrosion of metals. In small amounts, it is unpleasant but not dangerous. In
large amounts, it is harmful.
QM5204
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