DAIRY INSPECTION 195 



occur especially in limestone districts, in which basins or 

 sinks may be found on the surface which are connected 

 with underground water channels. Muddy water or 

 floating material in the spring after severe rains are 

 indications of the existence of these conditions. 



The safety of well water depends upon the purity of 

 the water at its source, which is the underground water* 

 and the protection provided against the entrance into the 

 well of contaminated water or polluting material. The 

 purity of the underground water in the case of a well 

 will depend upon the same conditions as control the 

 purity of springs. Contaminated water or polluting 



Cesspool 



FIG. 23. How springs may be polluted by subsurface drainage. (From Water Supply 

 Paper 255, U. S. Geological Survey.) 



material may enter the well through openings in the 

 curbing or casing and, in open wells, from the surface 

 also. 



The open or dug well is the type most commonly 

 found on farms because it is the most cheaply made and 

 the work can be done by ordinary farm labor. With 

 certain precautions, the dug well yields a satisfactory 

 supply of water, but as commonly constructed it is the 

 most dangerous of all sources of water supply. A dug 

 well may be contaminated by material seeping through 

 the ground and curbing, or entering from the top. 

 Stone, brick, or wood curbing usually contains crevices 

 which permit the passage of polluting material. Such 



