When an isolated unit is unable to use an established water point, the
commander or a designated individual (or group of individuals) must make a search of
the area for the best available source of water. The following principles should always
a. A source should be selected which is as free as possible from known
b. When several otherwise equally desirable sources are available, the water
that is easiest to purify should be chosen. Less disinfectant is required to purify water
from a clean supply than from a supply of more questionable quality.
c. The water intake or the point of supply of a surface source should be as far
away as possible from known sources of contamination. When a stream is used, the
intake preferably should be upstream from any source of contamination. In lakes and
ponds, it is generally desirable to locate the intake as far from the shore as practicable,
distance from the shore.
UNIT WATER PURIFICATION
a. General. When units are not able to obtain water from established water
points, they must obtain and treat their own water. When surface water is used, care
should be taken to avoid getting mud from the bottom or picking up floating sticks,
leaves, or other debris. Turbid or cloudy water should be settled before it is used. A
settling basin may be constructed by digging a trench, parallel to the stream bank, into
which the water may seep and remain still. Another method is to dig a short ditch from
one side of the stream leading to a basin where the water can stand and settle. After
the dirt has settled, the clear water must be disinfected. The entire reliance for
rendering the water safe for consumption is placed on the disinfection process. The
disinfectant most often used in purifying water for drinking and other domestic purposes
is chlorine. The compound normally used to chlorinate water in the field is calcium
b. Chlorination Requirements. Sufficient chlorine must be added to water to
produce a required chlorine residual after a 30-minute contact period. Standard
requirement for field water supplies is five parts per million (ppm) chlorine residual.
However, higher or lower concentrations may be prescribed by the command surgeon
on the basis of his knowledge of local diseases and environmental conditions. A Lyster
bag or other clean container may be used to hold water for chlorination.