68 George C. Whipple 



Example : Assume the total hardness of a water to be 79 parts per 



79 

 million ; then Z) = — = $7 . 90 per million gallons. 



This takes into account only the cost of soap used for domestic 

 purposes, and does not include the incidental losses and inconveniences 

 attendant upon the use of hard water in the household. These, if 

 they could be expressed in terms of dollars and cents, would probably 

 more than equal the cost of soap; therefore the above figures err on 

 the side of conservatism. 



TEMPERATURE. 



Everyone knows that warm water is unpalatable. When the tem- 

 perature rises above 60° F., people do not like to drink it without 

 cooling. The relation between the temperature of the water and the 

 per cent of objecting consumers may be represented by a curve based 



on the equation /> = , in which p equals the per cent of 



objecting consumers, and d equals the temperature of the water in 

 Fahrenheit degrees. According to this curve, no one would object 

 to drink a water which had a temperature of 45°, half the people 

 would object at 66°, and all would object at 75°. If it is assumed 

 that it takes one-half pound of ice per capita daily to cool the 

 water used for drinking during four months in the year, and that 

 ice costs 30 cents per 100 pounds, then the depreciation value due 

 to temperature would be equivalent to $5 per million gallons of 

 public supply for 100 per cent of objecting consumers, assuming the 



per capita consumption to be 100 gallons daily, otD = — X $5 = ^^ — ^— ^ 



in dollars per million gallons, in which d = the average temperature 

 during the four warmest months of the year. This may be considered 

 as the depreciation value due to temperature. The temperature of 

 ground waters seldom rises above 60° in the house taps even in 

 summer, and in cities supplied with ground water a large propor- 

 tion of the consumers do not use ice. Surface waters, on the other 

 hand, in the latitude of New York, generally maintain a temperature 

 of 60° or more at the house taps for at least four months of the 

 year. The temperature factor is an important one in many cases, 



