THE WATER SUPPLY IN DRY AREAS 443 



rain, sleet and snow and from sheet or free water found 

 at various depths. The natural sources of the former 

 are springs and streams. The artificial sources are cis- 

 terns, ponds, irrigating ditches and wells. The latter 

 is obtainable from wells of varying depth. It is be- 

 lieved that this free water exists everywhere beneath 

 the earth's surface, but in some instances it is so deep 

 that it is not practicable to reach it, for economic uses. 

 In instances not a few, it is found at depths not far be- 

 low the surface, and this is true of it in some instances 

 in areas that are unusually dry. 



Ground or free water is very abundant. It has been 

 claimed that this free water in the earth's surface should 

 cover it to the depth of 90 feet. If only a limited pro- 

 portion of this could be obtained everywhere without 

 too great expense, it would make possible the tillage 

 of all the arable land in arid and semi-arid regions, 

 providing the water was always of such a character as 

 to properly sustain plant life. 



In some instances subterranean waters are so im- 

 pregnated with foreign influences, especially soda and 

 salt, as to be unfit for use by humans, and yet they may 

 be taken with apparent relish and without injury by 

 live stock. In yet other instances the impregnation is 

 so strong that it will not properly sustain animal or 

 vegetable life. But usually such ground water is of the 

 purest and the best. The character of the water is influ- 

 enced, of course, by the substances through which and 

 over which it passes. 



The little that is known as to the whereabouts of 

 subterranean waters, linked with the fact that they do 

 exist not infrequently in very unlikely places, emphasizes 

 the benefit that would accrue from determining their 

 whereabouts. The expense that would thus be involved 

 would be so great that it could not be borne by in- 

 dividuals. It is a work that may be best done by the 



