4 CONSERVATION OF GROUND WATER 



eral types. Some problems pertain to entire ground-water res- 

 ervoirs, 1 where the rate of replenishment is inadequate to meet 

 the continuing demand. In this report these are classed as 

 reservoir problems. The second type, classed here as pipeline 

 problems, arises because of the inability of water to move 

 rapidly enough through earth materials to supply the demand 

 of wells, even though the ground-water reservoir as a whole 

 may have an adequate supply of water. The third type occurs 

 along watercourses, where there is an intimate relation be- 

 tween the water in the stream and that pumped from wells. 

 These are the watercourse problems. 



The serious problems of ground-water shortage are in areas 

 where water is pumped out faster than the entire ground- 

 water reservoir is replenished. Under these conditions the res- 

 ervoir is being emptied of water that may have taken decades 

 or centuries to accumulate, and there is no possibility of a 

 continuous perennial supply unless present conditions are 

 changed. Even more serious is the condition where salty or 

 otherwise unusable water flows into a ground-water reservoir 

 as the good water is pumped out, for these reservoirs may be 

 ruined before they are emptied. Nearly all these excessively 

 pumped reservoirs are in the arid regions, where precipitation 



i As the term is used in this report, a ground-water reservoir consists of 

 saturated rock materials sufficiently permeable that water can move through 

 them by gravity and can be withdrawn from them by wells. Characteristically, 

 water enters ground-water reservoirs by downward percolation from the land 

 surface in certain areas known as recharge areas, and moves laterally under- 

 ground toward areas of natural discharge, where it reappears at the surface. 

 The terms "aquifer" and "water-bearing formation" are commonly used inter- 

 changeably with "ground-water reservoir." The characteristics of ground-water 

 reservoirs are discussed further on pages 27 and 32. 



The term "ground-water reservoir" is used in a more restricted sense by 

 many writers to designate, for instance, the water-bearing formations under- 

 lying a city or other limited area, or the aquifers in which water is confined 

 under artesian pressure. Such limitations are especially common in detailed 

 studies of areas too small to permit analysis of the entire underground phase 

 of the hydrologic cycle (see page 33). On the other hand, some writers refer 

 to the "ground-water reservoir" of the United States as if all parts of the land 

 area were underlain by permeable rock materials. Actually, facilities for storage 

 of water underground are exceedingly variable from one geographic area to 

 another. 



