WATER SUPPLY FOR TROOPS 461 



The actual purification of the water in the field is usually 

 carried out in one of three ways: by heat, by filtration or by 

 chemical disinfection. To be satisfactory the process used should 

 comply Avith the following requirements: (1) it should be effi- 

 cient under field conditions with the sorts of waters which the 

 troops will encounter, (2) the apparatus and supplies should 

 be light enoug-h to be readily transportable, preferably without 

 the aid of wheeled transportation, (3) the rough treatment 

 likely to be received in the field should not throw the apparatus 

 out of adjustment or render it unsuitable, and (4) skilled at- 

 tendance should not be necessary to insure proper purification 

 since the operator may be incapacitated in service. 



There is no doubt that boiling offers the best means of render- 

 ing a polluted water safe. If the water is boiled for a few min- 

 utes nearly all bacteria are killed. A very small amount of 

 apparatus and material is required. In some cases, however, the 

 fuel is scarce or must be carried. The great disadvantages of 

 the method, however, are the amount of time consumed in heat- 

 ing up the water and cooling it, and the flat taste which the 

 water has unless re-aerated. In winter there is no trouble in 

 cooling the water, of course, and the cooling may be hastened 

 at other times 'by using porous jars, canvas bags or boilers 

 wrapped in burlap. The outer surfaces are moistened and the 

 evaporation of the water from the surface removes heat from 

 the vessel. In practice the cooling is usually done over night. 

 The vessels in which the cooled water is stored should be pro- 

 tected from dust and the men should never be allowed to dip 

 their water bottles into the water. Any infection of the water 

 will be followed by rapid bacterial growth since food conditions 

 and the lack of opposition favor rapid multiplication of bacteria. 



The heat-exchange sterilizer is an apparatus which has been 

 designed to do away with the time lost in heating and cooling 

 water in boilers of the ordinary sort. The apparatus is arranged 

 so that the cold impure water is used to cool the hot purified 

 water and at the same time effect a saving in heat. In order 

 to have the apparatus efficient and yet deliver the treated 

 water at a temperature near that of the raw water, the heat ex- 

 change surfaces must be as large as possible. This is accomplished 

 by bending a dividing wall into a sort of accordion pleating or 

 having the hot water pass through narrow tubes surrounded by 

 the cold, impure water. An apparatus of this sort is efficient 



