CITY WATER SUPPLY 



229 



out being filtered. The speed of the pumps is deter- 

 mined by the pressure of the water in the main pipes. 

 When a great number 

 of people are using water 

 the pressure in the pipes 

 is slightly reduced and 

 the pumps then increase 

 their speed, thus keep- 

 ing the pressure about 

 constant. 



(C) Combination of 

 the Pumping and Gravity 

 Systems. Cities located 

 in hilly parts of the 

 country use the tops of 

 some of the hills for 

 storage reservoirs for water. Standpipes also are usu- 

 ally located on some high point. The water is pumped 

 from wells or rivers into these reservoirs or standpipes 



FILTERING PLANT AND STANDPIPE 



SETTLING BASIN 



Water coming from the river 560 feet below. The chemicals are added 

 before the water comes out of these fountains. (Penn'a Water Co.) 



and then it is permitted to flow through the mains into 

 the houses by the force of its weight or gravity; thus 



