should be reduced when water temperatures are
less than 45°F.
The most important chemical characteristics of
water are its acidity, alkalinity, hardness, and
corrosiveness. Chemical impurities can be
either natural, man-made (industrial), or be
deployed in raw water sources by enemy forces.
Some chemical impurities cause water to
behave as either an acid or a base. Since either
condition has an important bearing on the
water treatment process, the pH value must be
determined. Generally the pH influences the
corrosiveness of the water, chemical dosages
necessary for proper disinfection, and the ability
to detect contaminants.
Hardness is caused by the soluble salts of
calcium, magnesium, iron, manganese, sodium,
sulfates, chlorides, and nitrates. The degree of
hardness depends on the type and amount of
impurities present in the water. Hardness also
depends on the amount of carbon dioxide in
solution. Carbon dioxide influences the volubility
of the impurities that cause hardness.
The hardness caused by carbonates and
bicarbonates is called carbonate hardness. The
hardness caused by all others (chlorides, sulfates,
nitrates) is called noncarbonated hardness.
Alkalinity is usually equivalent to the
carbonate hardness. Sodium, however, also
causes alkalinity. In natural waters, sodium is not
normally present in appreciable amounts.
Therefore, in natural waters, the alkalinity is
equal to the carbonate hardness. After
water has been softened, a large amount of
sodium remains in the treated water. In
softened water, the total alkalinity is the
sum of the carbonate alkalinity plus the
sodium alkalinity. Hardness is undesirable in
that it consumes soap, makes water less
satisfactory for cooking, and produces scale
in boilers and distillation units.
The following minerals cause hardness
in ground and surface waters:
l Calcium carbonate. Alkaline and only
lightly soluble; causes carbonate hardness
and alkalinity in water.
l Calcium bicarbonate. Contributes to
the alkalinity and carbonate hardness of
water. Calcium bicarbonate when heated
produces carbon dioxide and calcium
carbonate. This calcium carbonate
precipitates as scale ib boilers and
* Calcium sulfate or gypsum. Causes
noncarbonated hardness in water. Being
more soluble in cold water than in hot, it
separates from the water in boilers and
forms scale on the boiler tubes.
l C a l c i u m c l o r i d e . C a u s e s
noncarbonated hardness in water. In steam
boilers and distillation units, the presence of
calcium chloride causes chemical reactions
that can pit metallic tubing.