THE VALUE OF PURE WATER 69 



but it need not be used except when comparing surface waters with 

 ground waters. 



In a similar way it might be possible to calculate the reduced value 

 of a water due to other objectionable characteristics, such as the 

 presence of large amounts of iron or chlorine. Except in special cases, 

 these would not be as important as the more obvious qualities above 

 described, and they need not be considered in this discussion. 



SUMMARY OF PRINCIPAL FORMULAE. 



Depreciation due to sanitary quality 



i. # = 2.75 (T-N). 

 Depreciation due to physical characteristics 



2. 



100 



Depreciation due to hardness 



3" ~io 



Depreciation due to temperature 



4. D = -^ , in which 



D = the depreciation value in dollars per million gallons ; 



T= typhoid fever death-rate per 100,000; 



N= typhoid fever death-rate assumed to be due to causes 



other than water, and which may be ordinarily taken as 



20 per 100,000; 

 ^> c = per cent of consumers who object to the color of the 



water; 



p t = per cent of consumers who object to the turbidity of the 

 water ; 



po = per cent of consumers who object to the odor of the water; 

 c = color reading; 

 t = turbidity reading; 



