FILTERING OF DRINKING WATER 



225 



been in use for several years and are quite efficient if prop- 

 erly cared for. But in the ordinary home they are apt to 

 be worse than useless, since bacteria lodge in the porcelain 

 filter and grow there, so that the water passing through 

 will be actually contaminated in filtering. To prevent 

 this requires more careful attention 

 than will generally be given in a 

 house. The filtering cylinder should 

 be removed every day and carefully 

 cleaned by a thorough brushing, and 

 about every fourth day it should be 

 sterilized by boiling in water for five 

 minutes. This kills the bacteria in 

 the pores of the filter and renders 

 it safe for a few days. Unless one 

 is willing to adopt this plan of regu- 

 lar sterilization of the filter, it is 

 better not to use it at all. There 

 is no other means in the household 

 of filtering water which will remove 

 from it the danger of distributing 

 typhoid fever. There is a method 

 by which the water supply of a 

 whole city may be purified by filter- 

 ing on a large scale ; but this again 

 must be left to the public officials, 



and is not within the reach of the housewife. Her sole 

 method of purifying suspicious water is by boiling. 



Aerated Waters. The recognition of danger connected 

 with ordinary drinking water has led to the extension of 

 the use of a variety of aerated waters, Apollinaris ivater, 



f 



FIG. 76. Pasteur filter, 

 showing the filter itself, 

 a, made of unbaked 

 porcelain, and the metal 

 cover. 



