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.

WATERBORNE DISEASES

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

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 person's system. The time to grow is the incubation period.

Paratyphoid Fever

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

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 multiplies.