WATER SUPPLY AND SEWAGE DISPOSAL 159 



Some cities are so situated that it is possible for them to 

 secure water from mountain streams which flow from valleys 

 that are almost or quite uninhabited. The water of such 

 streams is usually of excellent quality and, if protected from 

 contamination by the inhabitants, will carry almost no disease- 

 producing bacteria. Since the lands in the mountain regions 

 are commonly of comparatively little value for agricultural 

 purposes, it has been possible for certain American cities to 

 acquire control of the entire drainage areas of the streams which 

 supply them with water (fig. 80). With proper care these 

 regions may be preserved from contamination and the purity 

 of the water insured. The United States Forest Service is 



1906 -- ^^^ 141 



!<.HI;- -^ -_---____ _^_^^^.^i:r> 



1908 ^^^^ "53 



1909 13 



1910 ^^12 



191110 



1912 6 



FIG. 81. Effect of purifying the water supply 



Diagram showing the typhoid death rate per hundred thousand population in Pitts- 

 hurgh, Pa., during a term of years. A filtration plant was installed in 1908 



cooperating with certain cities in preserving from contamina- 

 tion those parts of the reserves which drain into the streams 

 from which these cities derive their water supply. 



For many cities the only available source of water supply 

 is a river or lake which has become contaminated. In some 

 cases this water is pumped into the mains without any at- 

 tempt to remove or destroy the contamination. In these cases 

 the health of the people suffers and the death rate is abnormally 

 high (fig. 81). The citizen of such a city can protect himself 

 from the danger of polluted water only by sterilizing the 

 supply that he uses for drinking and domestic purposes. 



All cities that are properly organized and governed guard 

 the health of their citizens by proper attention to the quality 

 of their water supply. If this must be taken from a con- 

 taminated source, it can be purified by any one of several 



