THE VALUE OF PURE WATER 67 



Example: Suppose the turbidity of a water is 3, its color 65, and 

 its odor 2f (that is, faintly fishy), because of the presence of micro- 

 scopic organisms; then D = 20 - =$12 . 80; that is, the depre- 

 ciation value of the water, because of its unsatisfactory physical 

 qualities, amounts to $12 .80 per million gallons. 



HARDNESS. 



The point at which a water becomes objectionably hard has never 

 been exactly defined. Standards of hardness vary in different parts 

 of the country. The ordinary person washing his hands considers 

 the water soft if the soap will quickly produce a suds without 

 curdling. A hardness of 10 parts per million is practically unnotice- 

 able, and it requires a hardness of 20 or 30 parts per million to produce 

 ' curdling." Waters which have a hardness below 25 parts per million 

 seldom cause much complaint, but when the hardness rises above 50 

 the water is well entitled to the appellation "hard," and above 100 it 

 may be called very hard. In some parts of the country hardnesses of 

 200 or 300 are observed; these may be termed "excessive." 



In 1903 a number of experiments were made by the writer to deter- 

 mine the effect of various degrees of hardness on the amount of soap 

 used in washing the hands, in bathing, and in general household uses. 

 As a result of these experiments it was found that one pound of the 

 average soap as used in the household would soften 167 gallons of 

 water which had a hardness of 20 parts per million. This was equiva- 

 lent to about three tons of soap per million gallons, which at a cost of 

 5 cents per pound, would amount to $300 per million gallons. It was 

 found also that for every increase of i part per million of hardness the 

 cost of soap increased about $10 per million gallons of water softened. 



All of the water used by a community is not completely softened. 

 The number of gallons per capita per day completely softened has 

 been estimated by different authorities all the way from i to 10. It will 

 certainly be a conservative estimate to assume that one gallon per 

 capita is thus softened. On this basis the depreciation value of 



TT 



water, on account of its hardness, is D = , in which H equals 



the hardness of the water in parts per million, and D the depreciative 

 value in dollars per million gallons. 



