HOW WATER IS DELIVERED THROUGH CITIES 201 



plies by the same method. But the modern city must do 

 more than merely obtain water; it must deliver the water 

 to every part of the city and to the top floors of the tallest 

 buildings. Where cities obtain water from low levels they 

 are compelled to use pumps, or pumps combined with stand- 

 pipes or elevated reservoirs. The pressure of the water in 

 these standpipes or reser- 

 voirs forces the water to 

 faucets throughout the 

 city. The higher the sur- 

 face of the water is above 

 the outlets, the greater 

 will be the pressure (page 

 146). Largely on this 

 account water from a 

 standpipe or elevated 

 reservoir has a weaker 

 flow from faucets on upper 

 floors than from those on 

 lower floors of the same 

 building. 



Friction of running 

 water against the pipes 

 slows it up, and lowers 

 the pressure. For this reason a reservoir can serve only 

 a limited district. Large cities must provide many such 

 reservoirs. The necessity of furnishing water to the top 

 floors of very tall buildings and of fighting fire in these struc- 

 tures has compelled large cities to provide high-pressure 

 pumps in addition, to reservoirs. These pumps sometimes 

 keep the water in the mains of the business sections at a 

 pressure of 300 pounds, or even more, to the square inch. 



A STANDPIPE 



This furnishes water under high pressure 

 for the use of a community. 



