Figure 5-1. The pH scale.
A few substances have the capability to absorb any tendency of the water to
become acid or alkaline. These substances can conceal acid or alkaline
impurities. Therefore, if a pH test is made and if that test shows the water to
be neutral, there is no guarantee that the acid or alkaline impurities are
(5) Hardness. Hardness is caused by soluble salts in water (table 5-2). The
water. Hardness is undesirable in that it consumes soap, makes water less satisfactory
for cooking, and produces scale in boilers and distillation units.
(a) Oxygen. Large amounts of dissolved oxygen are found in
rainwater. The amounts in surface water vary. The oxygen, especially when carbon
dioxide is also present, causes many metals to corrode. Presence of game fish in
surface water is a good indication of high dissolved oxygen content.
(b) Carbon dioxide. Carbon dioxide enters the water from the
atmosphere, from decomposing vegetation, and from underground sources. It then
forms carbonic acid, which aids in the formation of bicarbonates of calcium and
(c) Hydrogen sulfide. Hydrogen sulfide gives water a rotten-egg odor.
It is also corrosive to metals. In small amounts, it is unpleasant; in large amounts,
hydrogen sulfide is also harmful. It is produced by decomposition of organic matter and
by breakdown of certain compounds containing sulphur. Water having a rotten-egg
odor quite likely contains sewage or large amount of animal or industrial wastes.