2. Offshore intakes. Offshore intakes are
sometimes required because of lack of time,
personnel, or equipment or because of coral con-
ditions 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 equip-
ment 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 con-
nect the rigid pipe on the sea bottom to the pipe
supported beneath the float.
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.
. Physicaldetected by one or more of the
. Chemicaldetected by chemical analysis
Biologicaldetected by testing for
. Radiologicaldetected by radiac equip-
ment and special laboratory field tests
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
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
. Taste (use with caution)
. 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 com-
bination of methods maybe most effective, con-
sider 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 in-
dustrial 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