suspended matter reduced to a level that makes the
water safe to drink or to use in preparing food.
Industries sometimes have to treat their raw-water
supply to meet the requirements of the manufacturing
processes. Boiler feedwater must often be treated to
prevent sludge from forming in the boiler and scale
from forming on the metal surfaces. Most towns and
municipalities must treat their water supply by some
method before distributing it as potable water. Water,
whatever the source, must be available in quantity and
quality to meet its intended use.
In this section, various diseases caused by the use
of water that is impure and unsafe are discussed. Some
of the methods of treatment and purification used in the
field to eliminate impurities in water are also
discussed. Additionally, you are introduced to types of
purification equipment with which you, as a
Utilitiesman, should be familiar.
Water flowing over the surface of the earth picks
up dirt, disease organisms, chemicals, and anything
else in its path that can be dissolved or moved. Water
that soaks into the ground loses many of its suspended
impurities, as it filters through the earth. Although the
water becomes clearer, it dissolves minerals and other
chemicals at the same time. Groundwater may be clear,
but it is not pure and may contain harmful disease
organisms and chemicals.
Waterborne diseases do not appear immediately
after drinking contaminated water. Disease-producing
organisms need time to grow and multiply inside a
person before they cause illness. The time between
drinking contaminated water and the appearance of the
disease is called the incubation period. Absence of
disease symptoms for several days after drinking
untreated water is no guarantee that the water is pure.
Lack of disease symptoms in the natives is no test
either, as they may have become immune.
IMPURITIES IN WATER
Any water supply can be a source of danger and
destruction because of the many impurities often found
in it. Impurities in water can be broken down into two
major categories -dissolved impurities and
suspended impurities. DISSOLVED IMPURITIES
are organic or inorganic materials or chemicals that
cause an unpleasant taste, color, or odor in the water.
SUSPENDED IMPURITIES include organisms as
well as organic and inorganic materials that usually
make the water turbid or muddy looking. Suspended
impurities are usually more dangerous to health than
dissolved impurities. The suspended impurities
consist of mineral matter, such as sand, silt, or clay; of
disease organisms, such as bacteria or protozoa; and of
water plants, such as algae. It is absolutely necessary to
remove or destroy the disease-producing organisms in
water that will be consumed by people.
TYPES OF WATERBORNE DISEASES
Water carries many of the organisms that produce
disease. Disease-producing organisms carried by
water occur in two classes-those readily destroyed by
chlorination and those that are chlorine resistant.
Although the chlorine-resistant organisms require
careful treatment, they can be destroyed by
purification methods. Waterborne diseases caused by
dangerous organisms include typhoid, paratyphoid,
cholera, amoebic dysentery, schistosomiasis, and
diarrhea. The following discussion stresses continual
care and inspection of the water supply, because
waterborne diseases spread if not treated properly.
TYPHOID FEVER is an intestinal disease caused
by the bacterium known as bacillus typhosus.
Symptoms of this disease are rose-colored eruptions of
the skin, accompanied by a high fever (lasting about 4
weeks) and frequent bowel movements. Typhoid fever
organisms are readily destroyed by field chlorination
methods. Most waterborne diseases do not appear
immediately after using contaminated water, as they
need time to grow after entering a persons system. The
time to grow is the incubation period.
PARATYPHOID FEVER is similar to typhoid in
sources of infection and in symptoms; the organisms
are, like the typhoid bacillus, readily destroyed by field
chlorination methods. The incubation period varies
from 4 to 10 days. An attack gives a person immunity
from a second attack of paratyphoid, but does not give
immunity from typhoid.
CHOLERA germs are discharged from the body in
feces where they live for several days. When water in
any form contacts this germ, it is carried along and