THE VALUE OF PURE WATER 



61 



where D stands for the loss in dollars per million gallons of water 

 used. 



Suppose the average typhoid fever death-rate for a community 

 which has a somewhat polluted water supply has averaged 43 per 

 100,000 for a period of five years, and suppose that for this place the 

 value of N is estimated as 15, then 



Z> = 2.75 (43 I 5) = $76.72 if the per capita consumption is 100 

 gallons. If the consumption per capita is 115 gallons, D would be 

 ^4ir f $76.72, or $66.71; if it were 63 gallons per capita, then D 

 would equal l - of $76. 72, or $121 . 77. 



The value of N must be naturally subject to local variation, and in 

 order to obtain an idea as to its probable value, a compilation of 

 typhoid fever death-rates has been made for cities and towns in differ- 

 ent parts of the country which use ground waters or filtered waters 

 that is, waters which may be considered as free from contamination. 



The following is a generalized summary of them : 



TABLE 3 . 



TYPHOID FEVER DEATH-RATES IN CITIES AND TOWNS WHICH HAVE GROUND-WATER SUPPLIES. 



There is reason to believe that the higher rates given above do 

 not correctly represent the situation, because in some instances the 

 ground water was supplemented by the occasional use of water which 

 may have been polluted. Proximity to a large city where the water 

 supply is contaminated was also responsible for some of the high 

 figures ; so also was the absence of sewerage systems. Nevertheless, 

 there seems to be a slight tendency for the typhoid fever rates to 

 increase in the United States from north toward the south in those 

 places where the water supply is reasonably safe. There are some 

 exceptions to the increase southward, however. Thus, in Camden, 

 N. J., which is supplied with a pure ground water, the typhoid rate 

 in 1901 was only 12, and 20 in 1902. 



