WATER SUPPLY AND SEWAGE DISPOSAL 163 



178. Methods of securing pure water. The cities on large 

 lakes have ordinarily taken their water supplies from the 

 lakes. They have sought to secure pure water by construct- 

 ing tunnels in the lake bottoms which make it possible to 

 secure water from points at a distance of from one to six 

 miles from shore. Even this distance is not great enough 

 to guarantee pure water in all cases, and filtering or other 

 means of purification is desirable. 



Some cities may 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. 81). 

 With proper care these regions may be preserved from con- 

 tamination and the purity of the water insured. The United 

 States Forest Service is cooperating with certain cities in 

 preserving from contamination 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 

 attempt to avoid contamination. The result is that the 

 health of the people suffers and the death rate is abnormally 

 high (fig. 82). The citizen of such a city can protect himself 

 from the danger of polluted water only by boiling 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 contami- 

 nated source, it can be purified by any one of several methods. 



