the water that is easiest to purify should be chosen. Less personnel and equipment are
required to purify water from a clean supply than from a supply of questionable quality.
(1) Ground water. Ground water is usually less contaminated than surface
water and is, therefore, a more desirable water source. However, this source is limited.
A ground water source (well or spring) should be at least 100 yards from sources of
contamination such as latrines or soakage pits. The water source should be higher than
the surrounding ground so that surface water drains away from the water source. (If the
water source is in a low area, drainage from latrines, soakage pits, and other sources of
possible contamination may contaminate the water.)
(2) Surface water. Although surface water is usually more contaminated
than other sources, it is commonly used in the field because it is generally more
accessible in the quantity required. 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 water should be obtained upstream from any source of
contamination. In lakes and ponds, it is generally desirable to take water as far from the
shore as practicable since the amount of contamination is usually higher near the shore.
SETTLING WATER FROM A STREAM
Turbid (cloudy) water should be settled before it is used. A settling basin may be
constructed by digging a trench parallel to a stream bank into which water from the
stream may seep and remain still. Another method is to dig a short ditch from one side
of a stream leading to a basin where the water can stand and debris can settle to the
bottom. After the dirt has settled, the clear water may be removed to a clean container
and disinfected by chlorination or by boiling.
When treating water at the unit and individual level, complete reliance is placed
upon the disinfection process. The disinfectant most often used in purifying water for
drinking and other domestic purposes is chlorine in the form of calcium hypochlorite.
Calcium hypochlorite is supplied in bulk and, also, in glass ampules that hold a half
gram of the substance. It is added to the water in the amount necessary to destroy all
of the pathogens (disease-producing microorganisms) presently in the water with some
chlorine remaining to serve as a continuing disinfectant.
a. Terms Used in Water Treatment. Some of the terms used in the treatment
of water are defined below:
(1) Water treatment. Water treatment refers to the removal of undesired
elements in the water to be used. Disinfection, coagulation, sedimentation, and filtration
are some of the procedures that may be used in water treatment.