MARGIN OF SAFETY 191 



ranging from 63 gallons to 1300 gallons were found in the 

 various reporting systems. 



If one looks through the list of cities and picks out those 

 as comparable as may be in population, location and amount 

 of manufacturing, with the one under discussion, a figure can 

 be selected which multiplied by the number of services will 

 give a first and very rough approximation of the amount of 

 water that can probably be sold. The amount of water used for 

 industrial and other uses from wells or other local sources must 

 be considered in making such comparison. 



A second approximation may be undertaken by subdividing 

 all the takers into three classes, following the classification of 

 the New England Water Works Association. 



Taking it up in this way in more detail, the second estimate 

 should be rather more accurate than the first one. This is par- 

 ticularly true if, as often happens, some of the larger takers are 

 already metered, and information can be substituted for esti- 

 mates for a part of the schedule. 



The statistics collected by the Committee on Meter Rates, 

 arranged to facilitate use in this way, are shown below. 



Domestic Services. In the first table are shown the domestic 

 consumers; that is to say, all those taking less than an average 

 of 820 gallons daily, or 10,000 cubic feet per quarter. 



The table shows for each system, first, the total number of 

 services, to give an idea of the size of the plant; second, the 

 percentage of services classified as domestic; third, the average 

 amount of water sold for each domestic service in gallons daily; 

 fourth, the total daily sales from the services classed as domestic, 

 reckoned on the whole number of services in the system. 



