UNDERGROUND WATER SUPPLY 459 
text-book, and based upon a single determination, and without reference to 
the position from which the sample was taken. 
But it is clear that systematic observation and experiment on the 
larger scale are required if we wish to estimate our underground water 
resources. 
There is much misconception of this problem in the mind of the general 
public, not to mention those whose business it is to recover and utilise 
underground water supplies. In recent months I have read numerous 
letters and special articles in the public press urging that we have under- 
ground in this country an inexhaustible supply of water. Instances are 
cited where a powerful spring or a large pumping station is yielding several 
million gallons of water a day, and, from a few such isolated cases in different 
parts of the country, it is argued that, if you bore down deep enough almost 
anywhere, there is the water in similar amounts asking to be pumped to 
the surface. 
I recently heard a very able and suggestive paper read before water 
engineers, in which the author advocated the extraction of underground 
water from comparatively shallow wells and boreholes in rural areas, 
utilising the power from the electric grid, in preference to the distribution 
of water from a regional source. ‘The vast extent of underground storage’ 
was a phrase used. 
Two important things must be borne in mind in this connection. First, 
if the underground water storage is drawn upon, as in times of prolonged 
drought, in excess of percolation from rainfall—if, in other words, the wells 
are continuously overpumped—it necessarily follows that the water-table is 
thereby continuously lowered while this excess lasts, thus depleting or 
drying up the shallower wells, and increasing the depth and cost of pumping 
the deeper wells. Not only so, but surface supplies from springs and streams 
are also depleted, to the detriment of lowland surface water supplies, canals, 
fisheries, agriculture, power stations, etc. Some folk have suggested that 
a national or regional scheme should be adopted, whereby the underground 
reservoirs are left practically intact, and their natural overflow allowed to 
feed surface springs and streams, and that the flood waters in upland 
regions collected in large reservoirs could be distributed by a widely spread 
system of pipe-lines, or ‘ grid,’ and so give an adequate supply to the whole 
community. As regards quantity, such a scheme does not seem ambitious, 
seeing that it has been calculated that the present domestic supply in the 
British Isles does not amount to more than about 1 per cent. of the total 
rainfall. But I must not be tempted to pursue this further, or even to out- 
line the difficulties as to cost, vested interests, and so forth, inherent in 
suchascheme. It is a matter of public policy and does not directly concern 
us here and now. 
It is well known that even in times of normal rainfall there are areas in 
and around some of our big cities, like London, where the underground 
water level is slowly and continuously falling, due to overpumping. One 
of the questions which call for investigation is that of these overpumped 
areas. The widespread impervious mackintosh of streets and houses 
aggravates the problem, by diminishing the natural percolation. 
In the second place, we geologists know well enough that large stretches 
of country are underlain by impervious and non-water-bearing rocks, such 
as the Keuper Marls of the English Midlands, and the Jurassic clay belts 
of the south and east of England. Borings through this impervious cover 
to depths, it may be, of many hundreds of feet may fail to tap water of 
potable quality. 
The underground storage is not inexhaustible, and there are many areas 
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