THE COST OF WATER 



339 



vated lake or stream serves as a natural reservoir, the cost of 

 the city's waterworks is practically limited to the laying of 

 pipes. But when the source of the supply is more or less on a 

 level with the surrounding land, the cost is great, because the 

 supply for the entire city must either be pumped into an arti- 

 ficial reservoir, from which it can be distributed, or else must 

 be driven directly through the mains (Fig. 208). 



RE&ERVOIR 



FIG. 208. Water must be got to the houses by means of pumps. 



A gallon of water weighs approximately 8.3 pounds, and 

 hence the work done by a pump in raising a gallon of water to 

 the top of an average house, an elevation of 50 feet, is 8.3 X 50, 

 or 415 foot pounds. A small manufacturing town uses at least 

 1,000,000 gallons daily, and the work done by a pump in 

 raising that amount to an elevation of 50 feet would be 

 8.3 x 1,000,000 x 50, or 415,000,000 foot pounds. 



The total work done during the day by the pump, or the 

 engine driving the pump, is 415,000,000 foot pounds, and hence 

 the work done during one hour would be ^ of 415,000,000, or 

 17,291,666 foot pounds; the work done in one minute would 

 be g 1 ^ of 17,291,666, or 288,194 foot pounds, and the work done 

 each second would be -$ of 288,194, or 4803 foot pounds. 



A i-H.P. engine does 550 foot pounds of work each second, 

 and therefore if the pump is to be operated by an engine, the 

 strength of the latter would have to be 8.7 H.P. An 8.7-H.P. 



CLARK INTRO. TO SC. 22 



