no DOMESTIC WATER SUPPLIES FOR THE FARM 



erally true as regards the shallower waters, which, being close to 

 the surface and without the protection afforded by overlying clays 

 or other impervious beds, are susceptible to pollution. Deeper 

 waters, on the other hand, are almost always overlain by rela- 

 tively impervious beds that serve to keep out polluting materials, 

 and as a rule they are entirely safe. In many places, however, 

 the amount of mineral matter dissolved in the water shows a 

 general increase with depth, the amount in deep waters averaging 

 several times that in surface waters, which are largely made up of 

 recent rainfall. There are some exceptions to this law, due mainly 

 to variations in the character of the materials in which the waters 

 are found, the waters in a calcareous glacial drift or in an alkaline 

 flat, for instance, often being very much harder than those in un- 

 derlying beds. Limestone waters, too, are generally harder than 

 sandstone waters. The maxim of certain drillers, "The harder 

 the rock the harder the water," is based on the prevailing softness 

 of the sandstones in many districts as compared to the hardness 

 of the limestones. 



Summary Statement. Contrary to the common belief, there 

 is no general increase in the volume of underground water with 

 increase in depth, such gain in volume as is occasionally found 

 being due to peculiar local conditions. Neither is there a univer- 

 sal increase of head, although it may happen because the lower 

 beds outcrop at higher altitudes than the upper ones (Fig. 32). 

 The deeper waters, however, are generally safer than those near 

 the surface, although their mineral content is likely to be higher. 



Protection of Deep Wells. Many of the conditions favorable 

 to pollution of the shallow wells likewise favor the contamination 

 of deep wells, but as the causes and remedies have already been 

 discussed, especially in connection with the section on "Safety 

 distance," they do not require further consideration at this point. 



The water of deep wells when first encountered is usually safe 

 and rightfully has a good reputation, so that people often go to 

 great expense in drilling for deep rock waters. Unfortunately, 

 however, many fail to realize that unless care is taken, it is possible 



