March 9, 1876] 



NATURE 



377 



what appear to be the strict limits of their Commission, It is 

 with their report that I am mainly concerned. 



The Commissioners have expressed their opinion that the 

 rivers Thames and Lea (or Lee, as the word is spelt in their 

 Report) ought to be abandoned as early as possible, and espe- 

 cially the former, as sources of supply to London. They regard 

 the condition of these rivers as hopeless, and point out that an 

 abundance of spring- and deep-well water can be procured in the 

 basin of the Thames and within a moderate distance of London ; 

 and they are further of opinion that the metropolis and its 

 suburbs should be supplied, on the constant system, exclusively 

 with this palatable and wholesome water. 



They believe that within forty miles of St. Paul's a suflScient 

 volume of deep-well and spiing-water can be obtained for the 

 present daily wants of the metropolis, but especially point to the 

 chalk and upper green-sand above the Gault, as the sources of 

 supply. They state that within thirty miles of London there is 

 an area of 849 square miles " covered" by these formations, and 

 that within 40 miles radius the area is 1,597 square miles. 



They estimate, to a great extent guided by experiments carried 

 on during many years under my superintendence, that the portion 

 of the annual rainfall upon this large extent of porous rock, which 

 sinks to reappear in springs and streams, may be taken at six 

 inches annually, and point out that this amount of infiltration 

 into the chalk area within thirty miles of the metropolis indicates 

 the quantity of 202 millions of gallons daily, as the theoretical 

 maximum supply available from that area. They suggest that 

 the greater portion of this water, which now escapes in springs 

 and in the river-beds at the lower levels of the absorbent (Ustrict 

 on which it falls, might be abstracted by a sufficient number of 

 wells sunk below the present spring-heads of the district, and so 

 constantly drawn upon, that there should always be a void for 

 the reception of unusual rainfalls below the level at which the 

 drainage of the district naturally escapes. They incidentally 

 admit that any water drawn from the subterranean reservoir in 

 the chalk by artificial means will be at the expense of the streams 

 which now flow through the valle) s in the chalk area, but do not 

 give even a passing consideration to the effect upon that area of 

 abstracting Irom it its natural supply of water, and conveying it 

 — "convey, the wise it call" — to London — should the scheme 

 they advocate ever be carried into effect. 



It can hardly be believed that a proposal such as this, involv- 

 ing the diversion of the whole of the water from the natural 

 springs and streams over an area of not less than 440 square 

 miles — an area larger than that of several English counties — 

 should have been brought forward without the slightest reference 

 to what would be the result upon this vast extent of coimtrj', the 

 inhabitants of which are to be sacrificed to the presumed needs 

 of this overgrown city. It will, I think, come within the pro- 

 vince of the geologist to point out not only where spring-water 

 of good quality is to be obtained, but also what will be the effect 

 of its abstraction upon the districts where it now exists in suffi- 

 cient abvmdance to overflow into the streams. It wiU be for him 

 to show what will be the efl'ect of producing " a void below the 

 level at which the drainage of the country naturally escapes ; " 

 how what are now fertile and even irrigated meadows will be 

 converted into arid wastes; how watercress beds, now of fabulous 

 value, will be brought to the resemblance of newly- mended turn- 

 pike roads ; how in such a district all existing wells, many of 

 them already some hundreds of feet in depth, will be dried, the 

 mill-streams disappear, and even the canals and navigable rivers 

 become liable to sink and be lost in their beds. And these 

 results would, if the scheme were carried out, not be confined to 

 some single spot, but would extend over hundreds of square 

 miles. 



It may perhaps be thought that I am exaggerating the size of 

 the area, the natural water-supply of which it is proposed to 

 abstract ; but the calculation may be readily verified. 



The quantity of water now daily supphed to London by the 

 different water- companies, exclusive of the Kent Company, which 

 already supplies deep-well water to the extent of 9,000,000 

 gallons daily, is stated to be 104,800,000 gallons. Ivow if the 

 supply of 6 inches of rainfall per annum, absorbed over 849 

 square miles, be, as the Commissioners calculate, equivalent to 

 202,000,000 gallons daily, it is evident that it will require more 

 than halt that area to furnish 104,800,000 gallons daily, the exact 

 figures being 440^ square miles. 



It must, however, be remembered that the Commissioners 

 regard this quantity as the theoretical maximum of water-supply 

 available from such an area. And they are right in so doing ; 

 for in some years a far larger area would have to be exhausted in 



order to produce so large a water-supply, since not unfrequently 

 the quantity of the rainfall which percolates to a depth of only 

 3 feet into the soU, instead of being 6 inches, as supposed in the 

 calculation, is as low as 3 inches. For three years running 1 

 have known the percolation through a depth of 3 feet of ordinary 

 soil covered with vegetation to have been on the average only 

 3^ inches, and through chalk under the same conditions, less 

 than 5j inches. It would appear then that it would be safer to 

 regard the available spring-water supply as not representing 

 more than 4 inches of the rainfall per anniun, instead of 6 inches, 

 in which case the area requisite to supply 104,800,000 gallons 

 daily would be 660 square miles. 



To avoid any possible error, let us look at the matter from 

 another point of view. One inch of rain falling over a statute 

 acre produces, as nearly as may be, ico tons, or 22,400 gallons 

 of water. Dividing this by 30 as representing the daily con- 

 sumption of one person, there would be enough for one person 

 for 743 days, or, say, for two for one year. Four inches of rain 

 would render each acre capable of supplying the wants of eight 

 persons, so that a square mile of 640 acres would supply 5,120 

 persons for one year. Calling the population of the metropolitan 

 area 4,000,000, and dividing that number by 5,120, we arrive at 

 an area of 7S0 square miles as necessary for their supply. 



There can therefore be no doubt as to the vast extent ot 

 country which the proposal of the Commissioners would place 

 under unnatural conditions with regard to its springs and 

 streams. 



No doubt wells may, in some few instances, be placed in such 

 a position as to affect but slightly the neighbouring streams. The 

 wells of the Kent waterworks, for instance, which supply 

 9,000,000 gallons daily, are so placed as mainly to derive their 

 supply from water that would otherwise find its way into the 

 Thames by springs along its bed ; indeed, from the amount of 

 chlorine present in the water, it may be doubted whether some 

 portion of it is not derived from the Thames itself by filtration 

 through the chalk. It seems probable that in the valley of the 

 Thames immediately above London there may be spots from 

 which a limited supply of water might be pumped without much 

 injury to the neighbouring property; but a ■wholesale abstrac- 

 tion of the entire supply of spring-water from an area of even 

 3C0 or 400 square miles could not be otherwise than most 

 disastrous. 



On looking at the actual chemical analysis of the waters sup- 

 plied by the different companies, as furnished by the Commis- 

 sioners, there would at first s'ght appear to be some difficulty in 

 understanding their reasons for so highly commending the Kent 

 Company's water, and so unhesitatingly condemning that of the 

 other companies, if we are to take as our guide the "previous 

 sewage or animal contamination," on which so much stress is 

 laid. It is hard to comprehend why, if river or flowing water 

 which exhibits any proportion, however small, of "previous 

 sewage or animal contamination," is to be regarded as suspicious 

 or doubtful, the water in wells, say lOO feet deep, may be 

 allowed io,oco pints in loo,coo, or i pint in 10, and may yet 

 be regarded as reasonably safe. For, in these deep wells, if at 

 no great distance from a river such as the Thames, it by no 

 means follows that there is not some amount of comparatively 

 direct commimicaticn through which water may trickle rather 

 than filter, and not improbably the river-water below London is 

 more objectionable for drinking purposes than it is higher up the 

 Thames. 



Let us for a moment compare the " previous sewage or animal 

 contamination " of the water supplied by the different companies 

 deriving their water from the 1 hames and Lea with that of the 

 Kent Company's water. I take the average of the different 

 analyses of each, as given at p. 270 et siq. of the Report : — 



West Middlesex 3083 



Grand Junction 3226 



Southwark and Vauxhall 2 '983 



Lambeth 3081 



Chelsea 2785 



New River (excluding 1868) ... 2751 



EastLondon 2*304 



Average 2*888 



Kent Company 6"48o 



or upwards of twice that of any one of the other Companies, 



In this average, however, is included the water from the 

 wells at Charlton and Belvedere, both of which are condemned 



