YVATFK SUPPLY FOR COUNTRY HOUSKS. 83 



no! be feared to extend deeply below (lie water surface in tin- strata. And this leads up to 

 an important consideration. \Yhcrc UK-IT is an\ risk, heavy pumping at any one point is 

 inadvisable. A heavy draught at one point creates a depression round the well if the supply is meagre, 

 and the impure top layers of water may be draw.&quot;, into that depression, as in Fi.n. lid. In Midi 

 conditions pumping must be. moderate, so as not to produce serious lowering about the well. II 

 the dotted line represents the less pure upper layer of water, it is clear from the diagrams how this may 

 or may not be drawn into the pumps according as these ate worked beyond or within the fair vield 

 capacity of the rocks. The extent ol this so-called cone ol depression de] ends upon the amount ot water 

 in the strata and upon the freedom with which it can flow to any pumped centre. Speaking generally, 

 the yield oi a wc-11 will vary with the square root of the depth lowered. Thus, it a pumping rate ot ioga.1. 

 per minute causes the water to lower iff., a supply of _&amp;gt;ogal. per minute would lower it .|ft., and ,;ogal. 

 would demand &amp;lt;)ft. of lowering. This shows how a heavy demand may produce a very depressed cone. 

 Usually this matter is not important, but it may become important in certain hydrogeological conditions, 

 and it is always desirable when undertaking a water supply to have the aid of an independent expert. 

 Practical well-borers are sometimes tempted to bore, much further than is necessary. On the other hand, 

 the practical man who is carrying out the work may also hesitate, to advise boring deeper when he really 

 should do so, tor his advice may appear interested. The independent expert can retrain undue 

 expenditure, and can advise additional expenditure as the true wants of a case demand. \Y. 11 Bom 11. 



