The Supply and Uses of Water 189 



Ideal supply. Natural highland watersheds often furnish 

 the best, safest, and most abundant supply. Mountain streams 

 and lakes in a drainage territory free from human habitation 

 and from possible pollution provide water requiring little or 

 no preliminary purification. The use of such a supply depends 

 largely upon the topography of the country and upon its dis- 

 tance from communities. The purchase of right of way, with 

 the construction of reservoirs and conduits, may cost millions 

 of dollars ; but the economic profit and the benefit to the public 

 may be far greater than the cost within a comparatively short 

 period of time. 



Mountain streams as supply. In mountainous regions 

 many communities secure an abundant supply of safe and useful 

 water from near-by streams. On the score of economy such 

 a water supply is decidedly satisfactory. It is usually clear, 

 odorless, tasteless, and free from dangerous impurities. This 

 is especially the case where the gathering grounds are not 

 occupied by human beings. Still there is need of constant 

 supervision of the source and means of supply, for through 

 human carelessness or ignorance the water may be polluted 

 and endanger health and life. A patrol, to prevent such acci- 

 dents, is too often carried out laxly and intermittently. 



The Los Angeles supply. Los Angeles, in southern California, 

 has gone, after careful calculation of the cost and profit, about 

 two hundred fifty miles into the Sierra Nevada Mountains to 

 secure an adequate water supply. On the eastern slope of the 

 mountains, the city secured control of a watershed many hun- 

 dred square miles in area, and more than four thousand feet 

 above the level of the sea. Here rains and melting snows feed 

 a river that formerly emptied into a dead lake called Lake 

 Owens. Great collecting reservoirs have been constructed and 

 are supplied by the river which has been turned into a new 

 channel just above the ancient lake. Thence through tunnels 

 that pierce the mountains, and through cement and steel con- 

 duits (Fig. 55) that cross the Mohave desert, the mountain 



