WATER SUPPLY 



257 



commonly known as the Abyssinian tube well, is the 

 cheapest and one of the safest. This well is made by 

 driving into the ground a water-tight iron tube, the lower 

 end of which is pointed and perforated. 



In case rocks and hard clay must be penetrated, or 

 great depth must be reached to secure water, the bored or 

 drilled well, piped from top to bottom with water-tight 

 iron pipes, will be found most satisfactory. 



Fig. 68. Soil strata. (From Harrington's "Practical Hygiene.' ) 



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. 68. 



The most dangerous well is the common dug well with 

 pervious walls and so located as to permit seepage into 



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