AMOUNT OF SEWAGE J>ER CAPITA 123 



Another factor, affecting the per capita consumption of 

 water, and particularly noteworthy because sewers to carry 

 the waste water are designed for the water-consumption at 

 some distant time in the future, is that there is a tendency 

 for all cities to increase the rate of per capita consumption, 

 as they increase in size. Fig. 29, from the Freeman Report,* 

 shows this tendency unmistakably, although the exact rate 

 varies largely in different cities and in a few cities the law is 

 apparently contradicted. Nor is this inconsistent with the 

 statement already made that there seems to be no relation 

 between the per capita consumption and the size of cities. 

 In any one city, the rate increases as the city grows, and the 

 figure would indicate that, as an average value for large cities, 

 the increase is about 30 gallons every 10 years. Even in cities 

 where meters are generally used, the law holds, though the 

 rate of increase is smaller. 



The possible effect of a general introduction of water-meters 

 and the effect of their use on the rate of consumption must 

 be considered also in predicting future water-consumption. 

 To actually say that a city in which water-waste has been 

 abnormal will instal meters and that, as a consequence of this 

 predicted action, the sewers may be made only a fraction of 

 the size otherwise necessary, would not be a safe engineering 

 venture. But the probable result of installing meters may 

 be pointed out and the consequent saving in the cost of 

 building sewers used as an argument in favor of their purchase 

 and use. Fig. 30, from Freeman's Report, f shows in a general 

 way the effect upon the per capita consumption of the use 

 of meters. The curve of the average is not exact, but is drawn 

 as summing up the general tendency and as a convenient guide 

 to the eye in studying the comparative effect of various per- 

 centages of meters in the different cities. The effect of meters 

 is unquestionably to reduce the careless waste of water that 

 occurs in about 25 per cent of the house-services. At first, 

 it has a tendency to reduce the reasonable consumption, but 



* Diagram No. 4. f p. 70. 



