BASIS OF ESTIMATES 139 



on an average from pipes that have been in use for a considerable 

 term of years under average conditions and excluding all large 

 leaks of such size that it might reasonably be anticipated that 

 they would be discovered by a proper system of investigation 

 and stopped. 



Following Dexter Brackett's basis, leakage at a rate of 

 3 gallons per twenty-four hours per lineal foot of lead joint 

 under 100 pounds pressure may reasonably be anticipated. 

 For 8-inch pipe that amounts to 3420 gallons per mile. Prob- 

 ably the average pressure is less than 100 pounds, and this 

 figure would be somewhat reduced, perhaps to 3000 gallons 

 daily per mile. With 95 services per mile, the average loss 

 is then equivalent to 32 gallons per service daily. 



The following calculation is made in very general terms 

 to give an idea of the significance of this leakage with reference 

 to the finances of the whole system and not with any idea of 

 reaching precision. 



If the water lost is worth 10 cents per 1000 gallons, which 

 may be taken as about the average wholesale rate, this loss 

 amounts to $1.17 per service per annum. If the investment in 

 the street pipes amounts to an average of $100 per service, and 

 if the interest on the investment (or the profit to a company) 

 and the depreciation and the repairs and maintenance amount 

 to an average of 8 per cent of the first cost, then the total annual 

 cost of maintaining the pipes to supply one service on an average 

 is 8 per cent of $100, or $8. The water normally lost by leakage 

 as estimated above adds 15 per cent to this to make up the whole 

 cost of distribution. In other words pipe leakage adds 15 per 

 cent more or less to the average cost of distributing the water. 



