Figure 4-20.Wet-barrel, or California, fire hydrant.
DISINFECTION OF WATER-SUPPLY
LEARNING OBJECTIVE: Understand
disinfection chemicals, methods, and
emergencies and their applications.
Understand the application of pipe supports
and insulation in water-supply systems.
Water mains, wells, filters, storage tanks, and
other components of a water-supply system become
contaminated during installation and repair. Flushing
the system to remove dirt, waste, and surface water is
the first step in disinfecting the water system, but it is
not a sufficient safeguard. To ensure a safe water
supply, you must thoroughly disinfect each unit of the
system before it is placed in operation. The chemicals
used in disinfecting a water-supply system are the
same as those used in disinfecting water; for example,
a hypochlorite solution or chlorine gas.
The chlorine dosage required to disinfect a unit
depends upon the contact time and the amount of jute,
untarred hemp, and organic chlorine-consuming
material present. Under average conditions, the
following minimum dosages are recommended:
The volume of water in the unit to be disinfected
must be computed before the chlorine dosage can be
estimated. Use the formula for finding the volume of
a tank (V = r2h) and divide the volume by 231 to
determine the number of gallons (231 cubic inches =
1 gallon). The volume of water in different sizes of
pipe is listed below.
Volume per foot of pipe
The following methods of applying disinfectants
should be observed:
Liquid chlorine is applied by portable gas
chlorinators. Chlorine cylinders should not be
connected directly to mains because water may enter the
cylinder and cause severe corrosion and hazardous