616 ANXUAL RKTORTS OF DEPARTMENT OF AGRICULTURE. 



even' State and in 90 per cent of the counties of the mainhmd United 

 States. 



The wafer supply is the limit inc: factor in the productiveness of 

 the soil and failure or shortaue of tlTe su])ply must result in cui'tailed 

 yields of cro])S. In the humid regions the seasonal rainfall is de- 

 pended upon for the water supply, but it is important that this should 

 be supplemented by the storage water held in the subterranean 

 reservoir. 



In arid and semiarid regions the subsoil water is possibly of greater 

 importance. The results of the well census have brought out several 

 generalizations that emphasize the importance of further study in 

 this direction. 



From the data collected it appears that the subsoil water level has 

 settled since the settlement and cultivation of the land and the im- 

 pression is general that the level is continuing to change at a rate 

 varying from region to region and ranging from a slight rise in 

 irrigated districts to a lowering of about 3.5 feet per decade in other 

 localities. The lowering was more rapid within the first generation 

 of settlement than later. 



The depth of water level below the surface varies considerably and, 

 in over 60 per cent of the wells and in most States on the average of 

 all wells, is within what is generally regarded as capillary reach of 

 the surface. 



The subsoil water is the store assuring against drought, and these 

 data indicate that the upper level of ground water is in general not 

 far from the limit of its availability for plant growth. 



From the information gathered it appears that the actual loss of 

 water is 10 per cent of the aggregate volume within the first hundred 

 feet of the surface — a national loss comparable with or exceeding the 

 destruction of forest or the waste of fuel supplies. In the light of 

 the relation of soil water to productivity, determination of the rate 

 of lowering of the water level and means for its prevention is of the 

 highest importance. 



Aside from the generalizations the inquiry has produced useful 

 data pertaining to domestic water supply and to the peculiarities of 

 wells and springs. . 



The investigation is pioneer work in a field of great importance 

 and will be followed up by carefully kept records of wells in different 

 localities. Unfortunately, owing to the illness and death of Dr. 

 W J ]\[cGee, who was in charge of the work, there has been a tem- 

 porary interrux^tion in the investigation. 



