254 CONSERVATION OF GROUND WATER 



or partly west of the 98th meridian, of such waters for domestic, 

 municipal, stock water, irrigation, mining, or industrial purposes. 



If current plans for complete utilization of water resources in 

 the arid regions are carried out, many streams that have been 

 navigable will discharge ultimately only enough water to dis- 

 pose of salts and other undesirable materials. 



Since the flow r of navigable streams is dependent on con- 

 tributions from numerous non-navigable tributaries, practi- 

 cally all surface-w r ater and ground-water developments in the 

 drainage basin may have some effect upon the use of those 

 streams for navigation. The constitutional priority of navi- 

 gation is therefore likely to become a hot issue. It already has 

 become so on the Missouri River. However, the interests of 

 ground-water users so far have come into direct conflict with 

 those of navigation only where navigation channels have been 

 dredged deeply enough to cause salt-water encroachment into 

 ground- water reservoirs (see pages 208-212). 



RIGHTS AND RESPONSIBILITIES IN PHYSICAL AND CHEMICAL 



properties of water. As show r n in Chap. V, only a small frac- 

 tion of the water used by man is actually consumed in that use. 

 For the rest only specific properties are used and the water is 

 then returned to ground-water or surface-water bodies, where 

 it may be used again, perhaps several times. Many users de- 

 pend to a considerable extent upon water already used by 

 others, particularly along large rivers. The chemical or physi- 

 cal properties are commonly changed by each use, and the 

 change is usually for the worse as far as downstream users are 

 concerned. If water is used for sanitation, it becomes unsani- 

 tary; if it is used for washing, it gets dirty; if used for cooling, 

 it gets hot; if used for irrigation or industrial processes, it be- 

 comes contaminated by soluble or suspended materials. 



Used water has been the subject of many controversies and 

 considerable legislation. As villain it has been the basis for 

 a large body of court decisions and statutes regarding pollu- 

 tion on the one hand and concerning damage to real property 

 on the other. Men have also fought for the right to use "re- 



