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NA TURE 



[April 30, 1896 



In the year 1832, and again in 1849, London was severely 

 visited by epidemic cholera, and the agency of drinking-water in 

 spreading the disease forced itself upon the attention of the 

 observant portion of the medical profession. It was Dr. Snowe, 

 however, who, in August 1849, first formally enunciated the 

 doctrine that drinking-water polluted by choleraic matters is the 

 chief mode by which cholera is propagated. 



In every visitation of Asiatic cholera to London, the water 

 supply was either altogether unfiltered or imperfectly filtered, 

 besides being derived from highly polluted parts of the Thames 

 and Lea ; and the enormous loss of life, amounting in the 

 aggregate to nearly thirty-six thousand people, can only be 

 attributed to this cause ; for it has now been satisfactorily proved 

 that cholera is, practically, propagated by drinking-water alone ; 

 and that efficient filtration is a perfect safeguard against its pro- 

 pagation. Moreover, it is most satisfactory to know that, since 

 the year 1854, no case of Asiatic cholera in London has been 

 traced to the use of filtered river water. The first effect of Dr. 

 Snowe's cardinal discovery was the removal of the intakes of 

 the river water companies to positions beyond the reach of the 

 tide and of the drainage of London. The second was the 

 greater attention paid to the efficiency of filtration. 



Such is the verdict in regard to cholera, and the same is true 

 of that other water-borne disease typhoid fever. But unlike 

 cholera, this disease is disseminated in several other ways, and 

 its presence or absence in any locality may not, of necessity, 

 have any connection with drinking-water ; as is strikingly shown 

 by the health statistics of Manchester, since the water supply of 

 this city, derived as it is from mountain sources, is above all 

 suspicion of this kind. These other causes have, during the 

 last ten years, been much mitigated in London by various 

 sanitary improvements ; whilst, as shown in the diagram on the 

 screen, there has been no corresponding mitigation in 

 Manchester. There is no evidence whatever that, since the 

 year 1869, when typhoid fever appeared for the first time as a 

 separate disease in the Registrar General's report, it has been 

 conveyed by the water supply of the metropolis. 



Although very soon after the year 1856, all the water supplied 

 to London was obtained from sources much less exposed to 

 drainage pollution, it was still very carelessly filtered. Previous 

 to the year 1868 there are no records of the efficiency, or other- 

 wise, of the filtration of the metropolitan water supply derived 

 from rivers ; but at that time, I began to examine these 

 waters for turbidity. In that year, out of 84 samples, 7 were 

 very turbid, 8 turbid, and 10 slightly turbid ; so that, altogether, 

 no less than nearly 30 per cent, of the samples were those of 

 inefficiently-filtered water. The metropolitan water supply 

 then, up to the year 1868, may be shortly described as derived 

 for many years from very impure sources with either no filtration 

 at all, or with very imperfect filtration ; and afterwards, when 

 the impure sources were abandoned, the supply was still often 

 delivered in a very inefficiently-filtered condition. But after the 

 establishment of monthly reports, the quality of these waters 

 gradually improved in this most important respect down to the 

 year 1883, since which time the efficiency of filtration of all the 

 river waters supplied to the metropolis has left little to be 

 desired. 



What is it, then, that separates the past from the present water 

 supply of London ? In the first place, there is the change of 

 source — I mean the change of the position of the intakes of the 

 several companies drawing from the Thames and Lea, and the 

 total abandonment of the much-polluted Ravensbourne by the 

 Kent Water Company. So long as the water was derived from 

 the tidal reaches of the Thames and Lea, receiving the drainage 

 of an immense population, the risk of infection from water-borne 

 pathogenic organisms could scarcely be otherwise than imminent ; 

 for, although we now know efficient filtration to be a perfect 

 safeguard, anything short of efficiency must be attended with 

 risk in the presence of such extreme pollution. 



Nevertheless, the line of demarcation between the past and 

 the present water supply of the metropolis is, in my opinion, to 

 be drawn, not when the intakes of the river companies were re- 

 moved to positions beyond the possibility of pollution by the 

 drainage of London ; but, it must be drawn at the time when 

 efficient filtration was finally secured and ever since maintained — 

 that is to say, in the year 1884. 



The removal of turbidity by sand filtration, however, refers 

 only to suspended matter ; but there are sometimes objectionable 

 substances in solution, of which organic matter is the most im- 

 portant. River water and mountain water, even when efficiently 



NO. 1383, VOL. 53] 



filtered, contains mure organic matter than spring or deep-well 

 water ; but this is reduced in quantity by storage and especially 

 by filtration, although it can perhaps never be brought up to 

 the standard of organic purity of spring and deep-well water. 



The Present Water Sui'ply. 



At present London is supplied with water from four sources : 

 the Thames, the Lea, the New River, and deep wells. Of 

 these, the deep wells yield, as a rule, the purest water, re- 

 quiring no filtration or treatment of any kind before delivery 

 for domestic use. The river waters, on the other hand, require 

 some kind of treatment before delivery — storage and subsidence 

 in reservoirs, and filtration. The water from the Thames is 

 abstracted at and beyond Hampton, that from the Lea is taken 

 out at two points, viz. at Angel Road near Chingford, by the 

 East London Water Company, and above Hertford by the New 

 River Company, who convey it to Green Lanes by an open 

 conduit twenty-five miles long, called the New River Cut, in 

 which it is mixed with a considerable volume of spring and deep- 

 well water. 



Hitherto I have spoken of chemical purity, or comparative 

 freedom from organic matter, only ; but the spread of diseases, 

 such as cholera and typhoid fever, through the agency of drink- 

 ing-water, has no connection whatever with the chemical or 

 organic purity of the water. These diseases are propagated by 

 living organisms of extreme minuteness, to which the names 

 bacilli, bacteria, microbes, and others have been given ; and 

 here comes the important question, how does filtration secure 

 immunity from these water-borne diseases. 



To Dr. Koch, of Berlin, we are indebted for the answer to 

 this question. By his discovery of a means of isolating and 

 counting the number of microbes and their spores in a given 

 volume of water, we were, for the first time, put into possession of 

 a method by which the condition of water as regards these living 

 organisms, before and after filtration, could be determined with 

 quantitative exactness. The enormous importance of this in- 

 vention, which was first made known and practised in England 

 in 1882 by the late Dr. Angus Smith, is evident when it is borne 

 in mind that the living organisms, harmful or harmless, contained 

 in water are of such extreme minuteness as, practically, to defy 

 detection by ordinary microscopical examination. But, although 

 the microscope cannot detect with certainty single bacteria or 

 their spores, even the naked eye can easily discern towns or 

 colonies consisting of thousands, or even millions, of such 

 inhabitants. 



Dr. Koch's method accomplishes at once two things : it 

 isolates, in the first place, each individual microbe or germ ; and, 

 secondly, places it in conditions favourable for its multiplication, 

 which takes place with such amazing rapidity that even in a few 

 hours, or at most in two or three days, each organism will have 

 created around itself a visible colony of innumerable members — 

 a town, in fact, comparable to London itself for population. By 

 operating upon a known volume of water, such as a cubic centi- 

 metre, for instance, the number of separate organisms or their 

 spores in a given volume of the water under investigation can 

 thus be determined. 



In order to ascertain the effect of filtration upon the bacterial 

 quality of the water, it is absolutely necessary that the sample 

 should be taken immediately after it has passed through the sand 

 filters ; for, if it be obtained from the delivery mains in town — 

 that is to say, after the water has passed through many miles of 

 pipes — the rapid multiplication of these organisms, except in 

 very cold weather, is such that a water which contains only a 

 single living organism per c.c. as it issues from the filter, may 

 contain 100 or 1000 in the same volume when, after several 

 hours, it arrives at the consumer's premises. 



Now, what is the effect of sand filtration, as carried out by the 

 various water companies supplying London, upon the living 

 matter contained in the raw river water ? It is simply astound- 

 ing — for water containing thousands of bacteria per c.c. (a single 

 drop of Thames water sometimes contains three thousand separate 

 living organisms) comes out from those filters with 50, 30, 10, or 

 even less of these organisms per c.c, or the number of microbes 

 in a single drop is reduced to 2, or even none. 



Rather less than one-tenth of the total volume of water 

 supplied to London is derived by the Kent Water Company 

 from deep wells in the chalk. As it issues from the porous 

 rock into the fissures and headings of these wells, this water is, 

 in all probability, absolutely sterile ; but by the time it has been'. 



