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 
Fic. 23.—How springs may be polluted by subsurface drainage. (From Water Supply 
Paper 255, U. 8. 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 
