WATER CONTAMINATION

Water takes on various characteristics and properties as it passes over and through the earth. These characteristics and properties vary and are dependent on the materials encountered. These materials may be natural or man-made and are classified according to their means of detection.

. Physical-detected by one or more of the human senses . Chemical-detected by chemical analysis

Biological-detected by testing for chloroform organisms . Radiological-detected by radiac equipment and special laboratory field tests

PHYSICAL IMPURITIES

Physical impurities in water are either suspended or dissolved. The suspended impurities are usually more dangerous to health. They include mineral matter, disease organisms, silt, bacteria, and algae. They must be destroyed or removed from water that is to be consumed by humans.

The most important physical characteristics are turbidity, color, odor, taste, and temperature. Valuable information can be obtained by observing the water with any of the five human senses and using commonsense judgment on the following characteristics:

l Color

. Turbidity

. Odor

. Taste (use with caution)

. Temperature

. Condition of vegetation around source

(dead or mottled vegetation can indicate the presence of chemical agents)

. Presence of dead fish, frogs, and so forth

Before starting any treatment to remove color, turbidity, taste, or odor, you should take several preventive measures.

You must prevent the formation of algae in raw water supply points. Algae can be controlled with copper sulfate, chlorine, or activated carbon. Before deciding which method or combination of methods maybe most effective, consider the following factors: 

. Volume of water to be treated 

l Time of year . The effects of treatment on fish life

. Type of secondary water treatment in use . Equipment available l Cost of treatment

You must also prevent the raw water source from becoming polluted by drainage from industrial waste and surface drainage from farms, mines, and watersheds.

The above conditions usually cause water to take on color due to the presence of colored substances in solution, such as vegetable matter dissolved from roots and leaves. Dissolved humus, iron, and salts could also be included. True color is due to substances in true solution, apparent color includes true color and substances suspension rather than dissolved. Color may also be caused by industrial wastes and turbidity. Color as such is harmless, but objectionable because of its appearance and the taste and odors sometimes associated with it.

Turbidity is a muddy or unclear condition of water caused by particles of sand, clay, or organic matter being held in suspension. Clay and silt remain suspended in water for the longest period of time because of their particle size and specific gravities. The removal of turbidity is essential to the production of potable water. Removal reduces water contamination, extends the time between backwashing of filters, decreases chlorine demand, improves disinfection, and enhances user acceptability of the finished water. Proper water treatment requires turbidity removal because suspended particles often contain organisms that may cause diseases.

Turbidity is removed by coagulation and sedimentation. Since the physical characteristics of raw water vary widely in different locations, dosages of coagulant chemicals must be determined at each water point to ensure maximum efficiency with minimal waste of chemicals. After coagulation and settling, the water should not have more than 20 percent of the original turbidity. Daily jar tests will help check the optimum chemical dosage required to meet this standard.

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