WATER AND ICE SUPPLY 339 
Water from the upper pervious stratum should be 
avoided wherever possible, even with wells of the kind 
just described. Especially is this necessary where the 
wells are shallow. The purest water is obtained by sink- 
ing the well through an impervious stratum, like that 
shown in Fig. 71. 
The most dangerous well is the common dug well with 
pervious walls and so located as to permit seepage into 
it from outhouses, barnyards and cesspools. Wells of 
this type are altogether too common on dairy farms. 
Fig.72.—Sources of Well Water Contamination. (From Bul. 143 Kan. 
Exp. Sta.) 
All wells, whatever their construction, must be provided 
with water-tight metallic or concrete covers to prevent 
the entrance of impurities into the shaft. 
ICE SUPPLY. 
Necessity of Ice. Where there is no equipment for 
