452 WATER SUPPLY AND SEWAGE DISPOSAL 



equally rapid-moving camel, which was the beast of burden in 

 the earliest Biblical times. For this reason practically all of 

 the world's commerce up to about a half-century ago was car- 

 ried on by water. 



For centuries, man has used the power of running water to 

 help him perform his labor It has ground his corn and wheat ; 

 it has sawed his lumber and run his looms when no other force 

 was available. 



Plant life as well as animal life is largely dependent upon 

 water for its very existence. From prehistoric times man has 

 used water from near-by streams to IRRIGATE his crops. 

 Some of the greatest nations of the past have lived on soil 

 where the natural rainfall was insufficient, and artificial water- 

 ing, or irrigation, was necessary. 



In each of these cases to which we have been referring, man 

 has made use of the visible supply of water, i.e., to the water 

 which stands or flows above the surface of the land. We shall 

 soon see, however, that the ground itself is a great reservoir of 

 water and that to this vast supply of hidden water man owes as 

 much, possibly, as he does to the visible supply. 



I. SOIL PHYSICS 

 GROUND-WATER 



529. The Source of Well Water. While it is true that upon 

 the frontier of civilization men still get their water supply from 

 streams, and while it is true that most large cities consume so 

 large an amount of water that they, too, are obliged to take 

 their supply from streams or lakes, still it is probable that in 

 the United States a larger number of people are using drinking 

 water from wells. Since wells are such a common source of 

 water supply, we may well ask, Where does the water come from 

 which we pump from our wells? 



There is no mystery as to where the water comes from in 

 certain seasons of the year. When heavy rains have been 

 frequent and the ground is soaked full of water, it is easy to 



