1-14. REVERSE OSMOSIS
Reverse osmosis wiII be discussed later in this chapter and in Chapter 5.
Common methods of disinfection used by the Army include the use of boiling,
iodine, gaseous chlorine, and chlorine compounds.
a. BoiIing. This method is used as a field expedient, when disinfecting
compounds are not available. Disinfection by boiIing requires that the water be held at
a rolling boiI for 5 to 10 minutes to kiII most of the microorganisms that can cause
intestinal diseases. For emergency situations, water boiled for even 15 seconds helps.
BoiIing as a means of disinfection has several disadvantages. Once the water stops
boiIing, the heat is no longer sufficient to kiII organisms that may be subsequently
introduced; therefore, there is no residual protection against decontamination. This is a
particularly serious deficiency in the field, where water is frequently transferred from one
container to another. Therefore, water must be stored in clean, dry, closed containers
to prevent decontamination. There is also no way to measure the degree to which
water has been disinfected by boiling. BoiIing also tends to leave water flat and
tasteless. This condition may be corrected by aeration, but in so doing, the chance of
recontamination is increased. An additional disadvantage of boiling as a means of
disinfection is that it requires fuel and equipment that may not always be available.
b. Iodine. Iodine is a very effective disinfectant and is used for individual water
purification because of its simplicity. One iodine tablet is used to disinfect a canteen
(1 qt/960 ml) of water or two tablets if the water is turbid or cold (40F). A total of thirty
minutes is needed to do this process, as described in Lesson 2. As a principal means
of disinfection, however, it has several disadvantages. Iodine tablets are not very
stable; they decompose when exposed to, moisture in the atmosphere. The most
serious deficiency of iodine as a disinfectant is that there is no current test for
determining iodine residual in the field. In addition, iodine gives water a taste and color
which many people find objectionable.
c. Chlorine. Because chlorine meets all of the desirable characteristics of an
ideal disinfectant to an acceptable degree, it has been adopted by the Army as the
standard disinfecting agent. Chlorination is the only acceptable procedure for routine
disinfection under normal conditions.
(1) Gaseous chlorine is the most effective form of chlorine for disinfection,
however, it has two disadvantages. Whereas chlorine at the proper concentration in the
finished water is nontoxic to man, gaseous chlorine is extremely hazardous. Excessive
concentrations in the air can be fatal. In low concentrations, the gas is extremely
irritating to sensitive tissues of the eyes, mouth, throat, and nose. Repeated exposures
may have a cumulative effect on lung tissues. Equipment used for chlorination with
gaseous chlorine is relatively complicated; therefore, only specially trained and reliable