WATER 



25 



who sink wells in any spot that happens to be most convenient to 

 them, without any regard to proximity of dangerous soil-washings, 

 and make the wells rubble-steined so as to let in as much of the 

 surface water as possible, the object, of course, being to save labour 

 and expense in deep sinking and in steining. But it must be clearly 

 understood that, because a well-shaft does not penetrate an im- 

 pervious stratum, the water collected is necessarily dangerous. A 

 shallow well, if sunk to a sufficient depth, which varies with the 

 nature of the soil, and has the upper part properly steined so as 

 to exclude the real surface water, may, and often does, provide a 

 water of excellent quality. 



The construction of the well is the all-important factor. 



Dr. Thresh says that, in the large majority of cases, where 

 shallow wells yield pol- 

 luted water it is due to 

 defects in the construc- 

 tion of the wells, and 

 for the guidance of 

 those about to sink 

 wells he points out that 

 the water which enters 

 at a depth of 6 to 12 

 feet, depending upon 

 the porosity of the soil, 

 is usually efficiently 

 filtered and purified ; 

 that water entering at 

 less depth is nearly 

 always liable to be im- 

 perfectly filtered and 

 unsatisfactory in qual- 

 ity ; and that the nearer 

 the ground surface at 

 which water can enter, 

 the greater the danger 

 of pollution. The upper 

 6 to 12 feet should be 

 water-tight and the top 

 should be so finished off 

 that no surface water 

 can possibly gain access. 



FIG. 1. Showing a Correct Method of con- 

 structing a Shallow Well (Thresh).* 



* The Examination of Waters and Water Supplies, by J. C Thresh, 1913, 

 J. & A. Churchill. 



