CITY WATER SYSTEMS 489 



in Illinois. The source of this water supply is at a somewhat 

 higher elevation; therefore, many of these wells are flowing 

 wells. London, Eng., and Brooklyn, N. Y., have in the past 

 secured a considerable portion of their water supply from w r ells. 



572. City Water must be under Pressure. The city is 

 fortunate which has its source of supply at a considerable 

 elevation above the level of the city. It is necessary that the 

 city supply shall be under pressure, not only in order that the 

 water may be used on the upper floors of tall buildings, but 

 also to aid in the fighting of fires. It is also of great service 

 that the water be under pressure in a city, for it may then be 

 used for power purposes. In many cities the elevators in 

 office buildings, stores, warehouses, and dwellings are operated 

 by water power. Water motors are frequently used where 

 small amounts of power are occasionally used, as in running 

 the family washing machine. All modern plumbing is con- 

 structed to be used in connection with a water system where 

 the water is under considerable pressure. 



Figure 300 shows the arrangement of the plumbing in a mod- 

 ern city dwelling. It will be seen that both city water and soft, 

 or cistern water, are provided. The city water being under 

 pressure is made to pump the soft water into the storage tank 

 in the attic. The hydraulic pump by which this is accom- 

 plished is generally called a WATER-LIFT. One-half of the 

 water-lift, the left half in the figure, is really a water motor 

 operated by the city water; the other half is a pump operated 

 by the motor and it pumps the cistern water. Such a water- 

 lift may be so constructed and installed that it will pump 1 gal. 

 of cistern water into the attic tank for each gallon of city 

 water used. Would this be possible if the attic tank were at 

 as great an elevation as the city standpipe? Explain. 



573. How Pressure is Maintained on the City System. 

 Most cities obtain their supply of water from a level lower than 

 the general level of the city. This is evidently the case with 

 all cities obtaining their water supply from rivers and lakes 

 upon the banks of which the cities are built. This must also 



