2. Offshore intakes. Offshore intakes are sometimes required because of lack of time, personnel, or equipment or because of coral conditions that prohibit well construction. Intakes of either the rigid pipe or float type may be used but they should be located in deep water beyond the surf. They must be positioned vertically and be off the bottom but still beneath the water surface at low tide. In this way foreign materials in the water which might cause excessive wear on equipment will be largely excluded. The rigid pipe intake can be placed on timber supports and anchored securely in position by piling or riprap. Floats securely anchored can support the intake screen in much the same manner as in surface waters. A rubber suction hose can be used to connect the rigid pipe on the sea bottom to the pipe supported beneath the float.

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:

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

Time of year

The effects of treatment on fish life

Type of secondary water treatment in use

Equipment available

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