208 WATER, HEAT, AIR, AND LIGHT IN THE HOUSE 



as in laundries, tanneries, slaughter houses, starch fac- 

 tories, sugar refineries, gas works, petroleum refineries, 

 dye works, paper mills, etc. The community as a whole 

 needs it for protection against fire, and to carry away its 

 sewage. 



Some cities pump water into "standpipes," or elevated 

 reservoirs, from which it flows, under pressure, into the 

 street "mains," and then into the houses; others use 

 force pumps of large capacity (cf. 42) ; others, still, have a 

 combination of both systems, using the reservoirs to assist 

 the pumps when there is the greatest demand for water, 

 as at meal-cooking time, or when there is a serious fire. 



In order to get enough water, great cities go to enormous expense. 

 The Romans built great aqueducts (Fig. 199) to bring water from the 



lakes of the Apennines to 

 Rome. New York City now 

 gets its water, through an 

 aqueduct, from the Catskills, 

 90 miles away. Denver is 

 fortunate enough to be sur- 

 rounded by mountains having 

 many streams of pure water; 

 this is allowed to flow through 

 pipes, by gravity, to the city. 

 Los Angeles gets its water 

 from mountains many miles 

 away. The cities on or near 

 the Great Lakes use lake water; but they take great care to prevent 

 the sewage from the city from polluting the water intended for the 

 city. Chicago has built an expensive ''Drainage Canal" to carry 

 water from Lake Michigan into the Illinois River, and thus to empty 

 the city's sewage into the Mississippi instead of into the lake system. 

 Inland cities usually get their water supply from a near-by stream; 

 but such water needs careful filtration. 



Fig. 199. 

 How water may be carried under a river. 



