272 CONSERVATION OF GROUND WATER 



exceed the safe yield — water levels have been lowered since the 

 first well was constructed — and discrimination must be made 

 on the basis of an adequate scientific study. 



The public should know also that man is not responsible 

 for all the fluctuations in "water tables," for precipitation is 

 the prime source of replenishment for all water resources, 

 and climatic variations have a profound effect upon the posi- 

 tion of the water table. Throughout most of the Nation the 

 precipitation was far below normal in several years of the 

 1930's, particularly 193 1 and 1934, and large areas experienced 

 severe drought. Records collected in that decade showed the 

 water table in large areas to have been several feet lower than 

 in earlier years. Those records are still being quoted in books 

 and articles published during the last two or three years, al- 

 though subsequent records in the same areas show that water 

 levels generally have risen appreciably since the end of the 

 drought. 



POSSIBILITIES OF MULTIPLE USE OF WATER 



The public is aware that the nation uses prodigious quanti- 

 ties of water; it should also know that most of that water is 

 not used up but remains a part of the water supplies upon or 

 beneath the land surface and may be available for further 

 use. These once-used waters create problems of contamination, 

 and largely because of them some rivers are not sought out 

 for additional water supplies, even though they may carry an 

 adequate volume of liquid. The serious pollution of such 

 rivers as the Delaware, Potomac, Hudson, Ohio, and New Eng- 

 land streams has led to organization of interstate commissions, 

 which have already initiated major programs for correction. 

 The possibilities of reclamation of sewage and industrial waste 

 water are being considered in many localities where water sup- 

 plies are limited, the reclaimed water to return to streams or 

 to ground-water reservoirs. 



There have been predictions that the Nation's great water 

 requirements must some day, perhaps within 25 years, force 

 us to obtain fresh water by distillation of the ocean. There is 



