WHAT WATER DOES IN SOILS 



43 



(figure 19). Their water is usually purer than that 

 of shallow wells, which are often within reach of 

 drainage from houses and stables, thus becoming un- 

 healthy, and causing typhoid fever. 



FIG. 19. An artesian well. The water gushes up out of the earth and is 

 carried off by the pipe at the left to irrigate the land. 



Ground water is sometimes found too near the 

 surface to permit of growing crops. Permanent bottom 

 water should not be nearer than five feet from the sur- 

 face, for from that depth plants can get through their 

 roots all the moisture they need without irrigation, and 

 still not have the roots kept too wet or too near the 

 surface. In the arid countries most trees are able to 



