Source: Snow, John. Med. Times and
Gazette, n. s. vol. 16, Feb. 13, 1858 (Part 1), pp. 161-162, Feb. 20, 1858,
pp. 188-191 (Part 2).
Drainage and water supply in connexion with the public health
By John Snow, M.D.
I was visiting a gentleman in the West of England some time ago, and he showed me the plan of the drainage of his house and garden. The drains received the proceeds from the water-closets of the house, and they were made to empty their contents into a brook, which flowed along the lower part of the grounds. I had observed that this brook turned a flour-mill in the estate, about a quarter of a mile lower down the stream, so I inquired whether the miller and his family had any other water for drinking and preparing their food besides that of the brook. The owner of the property replied that they had not. He said he had never thought of that subject, but he would try to get the miller some other water. I do not know whether or not he succeeded; and I have only alluded to the circumstance because it is an instance, on a small scale, of what is occurring nearly all over the country. In very many places the drinking water of the community is polluted by the drainage from water-closets, and the constituted authorities try, with more or less of temporary success, to procure other water.
None of the Water Companies which supply this metropolis have, for the last eighteen months, obtained any water which is polluted by the sewage of the town. Five of these Companies, however, still obtain water from the Thames, in the neighbourhood of Hampton and Thames Ditton, where the river becomes every year more impure, from the contents of the water-closets of houses and villages situated on its banks. It is probable, indeed, that from the subsidence of the water in large reservoirs, and from its filtration, it is incapable of communicating disease; but the inhabitants of London ought not to be satisfied with a probability on this point, they ought to have an absolute certainty that disease cannot be communicated by the water supplied to them. Except for the enormous quantity of water which is required to wash away the contents of water-closets, London would, no doubt, by this time have been entirely supplied with water from springs and wells at a distance, or from deep wells in the chalk formation under the metropolis.
The fact that water-closets cause the pollution of the rivers is not the greatest evil attending them, for rivers can never be entirely free from pollution; a greater evil is that they occasion the demand for such an inordinate quantity of water, that, in most cases, a supply from springs and wells cannot be obtained, and the polluted rivers have to be resorted to for the supply. Croydon and a few other towns of moderate dimensions are indeed supplied with water from deep wells, and Manchester and two or three towns in Scotland are supplied with surface water from extensive uncultivated moors; but a great number of towns are supplied with river water, which is more or less liable to pollution according to the situation at which the water is taken, and which is constantly becoming more impure, from the increasing adoption of water-closets, even in rural districts.
A great part of the water supply of most towns, and almost the entire supply of the rural districts, is derived from pump-wells, which are often very shallow, and are extremely [161/162] liable to be polluted. It is my opinion that the absence of drainage, and its defective condition, are injurious to health only by the contamination they cause to pump-wells, or other supplies of water; and that when the health of the community is improved by improved drainage, either in town or country, it is by the amendment which is effected in the drinking water of the locality. I believe also that houses situated on gravel are generally more salubrious than those situated on clay, because organic matters are usually oxidized in passing through the gravel, and converted into mineral substances, chiefly nitrates, which have not the power of communicating disease. It is only when the source of pollution is very close to the pump-well that the gravel does not oxidize the organic matter.
I consider that the ordinary opinion which attributes the illness caused by absence, or imperfection of drainage, to effluvia given off into the air, is altogether a mistake. My reasons for this view of the subject are as follow. In the first place, whenever I have been able to separate the effluvia in question from real causes of disease, I have found an absence of effect. During the cholera year 1854, for instance, the Fleet-ditch was open for a considerable distance, and was covered in during the summer of 1855. The part open in 1854, and previously, passed through portions of the sub-districts of Saffron-hill, of the north sub-district of West London, and of St. James's, Clerkenwell. Now the mortality from cholera, in the Saffron-hill sub-district, was only at the rate of five in 10,000 inhabitants. The mortality in St. James's, Clerkenwell, was only eleven in 10,000; and the mortality in the north sub-district of West London was only five in 10,000, when the deaths in St. Bartholomew's Hospital are deducted.
In 1849 a part of Bermondsey, called Jacob's Island, was surrounded and intersected by ditches as wide as an ordinary canal, and covering several acres. The ditches were usually kept full, and emptied only at intervals. The water of the Thames admitted into them received the sewage of the surrounding population, either directly, from privies which over-hung the ditches, or through kennels and drains. A number of the inhabitants of Jacob's Island, and the streets immediately surrounding the ditches, had access to no other water except that of the ditches. They usually allowed it to stand awhile, for a sediment to subside, before they drank it. The Metropolitan Commissioners of Sewers caused an inquiry to be made, at the end of the epidemic of 1849, into the effect of using the water of these ditches; and Mr. John Grant, the Assistant Surveyor to the Commissioners, was kind enough to favour me with the result. In the streets inclosed by the ditches, and immediately surrounding them, there were 7,286 inhabitants. Of these there were 865 individuals having no other supply of water than the ditches, and the remaining 6,421 had the supply of the Southwark and Vauxhall Company, or were supplied by private pumps. During the first nine months of 1849, 18 deaths took place from cholera, and eight deaths from other causes, amongst the 865 persons having no water supply but that of the ditches; and 95 deaths from cholera, and 46 from other causes, amongst the 6,421 persons having another supply. The mortality from cholera was, consequently, at the rate of 208 in 10,000 amongst the persons using ditch water, and 147 in 10,000 amongst the inhabitants who had the supply of the Southwark and Vauxhall Water Company, or that of private pumps. The mortality of the population living amongst and around the ditches, but not drinking the water, was, in fact, almost exactly the same as that of the other inhabitants further removed from the ditches, whilst that of the people who were obliged to drink the water was more than one-third higher, as is shown by the following figures from the report of the Registrar-General. St. James's, Bermondsey, in which Jacob's Island is situated, suffered a mortality from cholera of 142 in 10,000; St. Mary Magdalen, Bermondsey, a mortality of 159 in 10,000, and the Leather Market sub-district of Bermondsey, a mortality of 160 in 10,000. It is proved, therefore, that the population of Jacob's Island did not suffer in their health from the effluvia of the ditches amongst which they lived.
Between the cholera of 1849 and that of 1854, the ditches about Jacob's Island were all filled up, and the late Mr. Chas. Walsh reported that the cholera on that spot was not worse in 1854 than in the surrounding district. Bermondsey suffered more from cholera in 1854 than in 1849, owing to the Thames water, with which it was supplied, having become more impure in the interval. The greatest covering in or filling up of open sewers or ditches which had taken place anywhere in the Metropolis was in St. James's, Bermondsey; and yet the mortality from cholera in 1854 was 192 in 10,000, being higher than in any other parishes in the south districts of London, except St. Saviour's and St. Olave's, which had the same water supply, and contain also the two large Hospitals.
Mr. Glaisher, in his Report on the Meteorology of London, in relation to the cholera epidemics of 1853 and 1854, expresses his opinion that the disease was increased by the impure exhalations from the river Thames. An examination of the subject in detail does not, however, confirm this opinion. There are seven registration sub-districts situated at the river side, and extending from the sub-district of Charing Cross to that of the south-east sub-district of the City of London inclusive, and every one of these sub-districts had a mortality from cholera, in the epidemic of 1854, considerably below the average of that of the Metropolis. The gross population of these sub-districts was 86,815 in 1851, and the mortality from cholera in 1854 was 203, or 23 in 10,000; that of the entire Metropolis being 45 in 10,000. These seven sub-districts are supplied with water by the New River Company. The sub-districts situated at the river side on the south of the Thames had generally a high mortality from cholera, because they were chiefly supplied with unfiltered water by the Southwark and Vauxhall Company from the river at Battersea; but the sub-district of Lambeth Church, first part, which extends along the river side from Westminster-bridge to Vauxhall-bridge, and was chiefly supplied by the Lambeth Company with water from Thames Ditton, had a mortality from cholera of only 29 in 10,000. It should be observed, also, that districts situated at a good distance from the river had a high mortality, when they were chiefly supplied with water by the Southwark and Vauxhall Company. Thus Walworth, which is from a mile to a mile and a half from the Thames, had a mortality of 131 in 10,000; and Camberwell, more than two miles from the river, had a mortality of 136 in 10,000. Mr. Glaisher tries to explain this high mortality at a distance from the river, by supposing that the exhalations are confined by the neighbouring high grounds; but in another part of his report (p. 23), he has shown that Camberwell is beyond the influence of the Thames and the thick atmosphere of London, and that it enjoys a meteorology similar to that of the country near London. There is no situation in which the exhalations from the Thames would be more liable to be confined by the neighbouring high ground than in the valley of the Fleet river or ditch; and in 1854 this ditch was uncovered for a great distance, and was much more impure than the Thames, yet the districts in its neighbourhood suffered extremely little from cholera, as was before stated.
The fact that persons who work habitually amongst offensive animal substances do not appear to suffer in their health, confirms the view that no material injury arises from the effluvia of sewers and drains. The accompanying table, No. 1, contains the mortality in 1851 amongst persons occupied in certain offensive trades in England and Wales, from the Fourteenth Annual Report of the Registrar-General. These trades comprise the second and third sections of the twelfth class of the Registrar-General, and comprise all the persons working in grease, bones, intestines, skins, hoofs, and horns. The deaths are arranged in decennial periods; and I have taken from the census report of the same year the number of persons living in these trades--both the entire number of 20 years and upwards, and the number living at each decennial period, and have calculated the deaths per thousand for each period of life. I have also done the same for males of all occupations, so as to draw a comparison between the population occupied in offensive trades, and the entire population of grown-up males. It will be observed that in the whole population of males of 20 years and upwards, the mortality was 20 per thousand in 1851, while among persons employed in offensive trades it was only 18.3 per thousand. In other words while the entire adult male population had an average duration of life of 50 years, the average duration of life in the offensive trades was 54 years and seven months. At each decennial period under 45 the proportion of deaths is considerably less in the offensive trades than in the rest of the male population; from 45 to 55 the mortality is precisely the same in both; and at ages above 55 it is slightly higher in the offensive trades. [162/163]
The material among the emanations from drains and sewers which is supposed by many persons to be most active in promoting zymotic disease is sulphuretted hydrogen gas; but it must be acknowledged that the chemist never catches any disease from this gas, when liberated in his laboratory; and that invalids drink a solution of it at Harrowgate and other places, without acquiring any tendency to zymotic disease, although the gas is undoubtedly absorbed into the blood. An instance occurred lately of this gas being set free on a very large scale, without its doing any injury to health. It is as follows:--
"At a certain point in Westerdale Head (North Riding) the process of jet-mining has been carried on for some time past, and a few weeks since it was observed that the heaps of shale excavated or turned over by the miners were giving out much smoke, and the smoke was accompanied by a noisome smell or stench. This smell, which is that of the sulphuretted hydrogen gas liberated from the decomposing alum shale, has been perceived at points not less than seven or eight miles, or even more, from the point of its origin; and every room in houses three or four miles distant is most offensively penetrated by it at all hours of the day and night. The burning heap is of large dimensions; many thousands of tons of the displaced shale lie in heaps more or less continuous. . . . It had been surmised that a mischievous effect on the health of the neighbourhood would be produced; but so far beyond the nauseous, suffocating fumes, which annoy everybody for miles in the direction of the wind from the burning heap, no harm seems to have been done; and it may be hoped, therefore, that none will now arise. Even among the inhabitants of the houses in the neighbourhood of the place no worse consequence than the annoyance from the almost intolerable stench has so far arisen."--Times, 7th January, 1858.
It is quite true that sulphuretted hydrogen will cause sudden death when breathed in a too concentrated state, but no argument ought to be adduced from this circumstance with regard to its causing illness, for carbonic acid gas will also cause sudden death, although it is a normal constituent of the atmosphere.
I have in former papers, in this Journal and elsewhere, been able to point out the very close connection which exists between the mortality of cholera and the contamination of the drinking water, by the contents of sewers and cesspools. It has very frequently been observed, that cholera was most fatal in situations where the ordinary mortality was highest; and, taking both these circumstances into consideration, there was reason to presume that the kind of pollution of the water mentioned above increased the ordinary mortality, at times when the cholera was not present. I am now able to show, from a set of statistics compiled and calculated from the Quarterly Reports of the Registrar-General, that this is the case. That part of this metropolis which is situated in the county of Surrey is supplied with water by two companies [188/189]--the Lambeth Company, and the Southwark and Vauxhall Company. No other company supplied any portion of the metropolitan part of Surrey, except a very small portion of Rotherhithe, which is supplied by the Kent Waterworks Company.
The estimated population supplied by the Lambeth Company in 1854 was 166,906, and that supplied by the Southwark and Vauxhall Company 268,171. These numbers leave about 65,000 persons who were probably supplied by pump-wells, and lived chiefly in the more suburban districts, as Clapham, Wandsworth, Camberwell, and Norwood. The Lambeth Water Company, which supplied about one-third of the population of the metropolitan part of Surrey, obtained their water from the Thames in London, near the Hungerford Suspension Bridge, until January, 1852, when they moved their water-works to Thames Ditton, beyond the influence of the sewers of London. The Southwark and Vauxhall Company, which supplied more than half the population of that part of London which is situated in the county of Surrey, continued to obtain water from the Thames, between Vauxhall and Battersea, until July 22, 1855, when they obtained their supply from near the village of Hampton. I have shown, in the Table No. 2, the mortality in that portion of London which is in the county of Surrey, in every quarter of each year, commencing with 1850, and extending to June 1853, shortly after which period the cholera made its appearance. I have omitted the latter part of 1853 and the year 1854 from the table, as the cholera was present, and the mortality from this disease in this part of London has already undergone a very extensive and minute inquiry, extending to particular cases. Moreover, I do not wish on this occasion to inquire into the effect of water-supply on cholera, so much as on other diseases. The statement of the mortality in the table is, therefore, resumed at the beginning of 1855, and continued till the end of 1857. Throughout the table the mortality of the remainder of the metropolis during each year, and each quarter of a year, is shown side by side with that part of it which is situated in the county of Surrey.
It will be observed that in the years 1850 and 1851 the mortality of the metropolitan part of Surrey was considerably above that of the rest of the metropolis, being 1.8 per 1,000 above it in 1850, and 1.5 above it in 1851. In 1852, when a part of the water-supply of that part of London had been improved, the mortality still remained greater than that of the rest of the metropolis, but to a less extent than in the two previous years, only exceeding it by l.2 per thousand. In the first half of 1853, the mortality of the metropolitan part of Surrey exceeded that of the rest of London by only decimal 4 [0.4] per 1,000, or at the rate of decimal 8 [0.8] per 1,000 per annum. When the account of the mortality is resumed in 1855, after the cholera had passed away, it will be observed that the mortality of the metropolitan part of Surrey is still above that of the rest of London, in the two first quarters of the year; but on the 22nd of July, the Southwark and Vauxhall Company changed their source of supply from Battersea Fields to a point near Hampton, beyond the reach of the contents of the London sewers; then the whole of the metropolitan part of Surrey had an improved supply of water, and then, for the first time within the period of my inquiries, the mortality of this division of London falls, in that very quarter of the year, below the mortality of the remainder of the town. It remained below it in the last quarter of 1855, and also in the years 1856 and 1857, taking the mortality by the year together; and there are only two separate quarters in which the mortality of the Surrey Division of London rose a very little above that of the rest of the metropolis. I have not made any corrections for increase of population, because that of the metropolitan part of Surrey increased, from 1841 to 1851, exactly in the same ratio as that of the rest of London, and therefore the relative mortality of the respective divisions would have remained the same in the table, if the correction had been made.
The Chelsea Water Company removed their source of supply [189/190] at the end of June, 1856, from Chelsea to a point of the river beyond the influence of the tide, and the mortality of the Chelsea and Westminster districts, which are supplied exclusively by this Company, has diminished in comparison with that of the rest of London. The diminution is, however, not so great as in the districts supplied by the Southwark Water Company, for the Chelsea Company used to separate a great past of the impurity from the water by subsidence and filtration before its distribution.
I have not had an opportunity to inquire into all the diseases besides cholera, which have been diminished by the improvement of the water supply; but I find that, since the change in the source of supply of the Southwark and Vauxhall Company, there has been a marked diminution in the deaths from diarrhœa and typhus, in the districts they supply. Since the commencement of 1855 the weekly reports of the Registrar-General have contained the deaths from these two diseases in the different districts of London, and I have compiled, in table No. 3, the numbers of deaths from diarrhœa and cholera as they occurred respectively in that part of London situated in Surrey, and in the rest of London, from the beginning of 1855 to the end of 1857. It will be observed that in the two first quarters of 1855 the mortality both of diarrhœa and of typhus was higher in the metropolitan part of Surrey than in the rest of London; but that in the next quarter, that in which the supply of water was altered, the mortality of diarrhœa in this part of London fell below that of the rest of the town, and remained below it, with only two trifling exceptions to the end of 1857. The mortality of typhus in the Surrey part of London fell below that of the rest of the town, not in the quarter when the supply of water was improved, but in the following quarter, and has remained greatly below it ever since. I ought to remark, that the Registrar-General includes typhoid fever under the term of typhus.
I have in former papers adduced proofs that polluted water does not increase the prevalence of cholera by its acting in a general way, but only by conveying the special morbid poison of the disease, which must be present in the water, from a previous case or cases of the same malady. So, when polluted water increases the prevalence of other diseases, we must conclude from analogy that it acts in a similar manner, and that, when the water formerly supplied by the Southwark and Vauxhall Company increased the prevalence of diarrhœa and typhus, it acted by conveying the morbid material of these diseases from former patients.
The injury caused by impure water is by no means in proportion to the amount of impurity, but rather in proportion to the number of person who respectively contribute to, and partake of that impurity. Thus a pump-well supplying a single family may be grossly polluted for years, without causing or communicating any illness, and if it do so at last, the illness may not spread beyond the family. Or a pump may supply a large population, but if polluted only by the cesspool of a single house, may be a long time before it does any harm; like the pump-well in Broad-street, Golden-square, which caused no mischief during three epidemics of cholera, but caused a great mortality in 1854. It is when a river receives the excretions of a town and at the same time supplies the population with water that the mortality is greatest, as shown in Hull during the cholera of 1849; at Newcastle and Gateshead during the cholera of 1853, and in certain extensive districts of London in every epidemic. And that increase of mortality which is so striking in time of cholera goes on to a less extent at other times.
It follows from what I have said above that I should recommend the discontinuance of water-closets, or at least their diminution, instead of the continued increase of their numbers. A complete and well-regulated water-closet is so great a convenience that one cannot expect it to be discontinued in the better class of houses; but the so-called water-closet used by the working classes, who form the great bulk of the population, is according to the experience I have had, a worse nuisance than an open privy over a cesspool; as the recent excrement sticks about the pan and pipe, and is constantly disturbed by the water. In recommending the diminution of the number of water-closets, I of course do not suggest a return to the use of common cesspools; but some kind of moveable tank might be contrived, which should be charged with peat, or charcoal, or sawdust, or some other substance which would have the effect both of deodorizing the excrement, and bringing it into a state of disintegration, in which it could be more easily applied as manure. The tanks should be of a uniform size, so that a full one could be replaced by an empty one. It would be in new houses, and new neighbourhoods, that a plan of this kind could be best introduced. Dr. Hawkesley has contrived a plan for deodorizing the contents of water-closets, but he retains the use of the water.
As I have said above, the greatest evil of water-closets is the inordinate demand for water they occasion, and thus prevent most large towns being supplied otherwise than from the polluted rivers. If the general use of water-closets is to continue, and to increase, it will be desirable to have two supplies of water in large towns, one for the water-closets, and another, of soft, spring, or well water from a distance, to be used by meter, like the gas. Another evil of the general [190/191] adoption of water-closets is the waste of manure. The sewage becomes diluted with such an enormous quantity of water that it is doubtful whether it can ever be profitably applied to agriculture. The quantity of the sewage is so great that it could not be detained in reservoirs, and it could not be constantly applied, as the ground is often oversaturated with rain; whereas, if the solid excrement were conveyed away in carts, by some plan similar to the one I have mentioned, the house drainage, which would contain a good deal of the urine of the community, together with solution of soap and other fertilizing materials, would be so moderate in amount that it might probably be applied as liquid manure. It would most likely be five times more fertilizing than the present sewage. By the present plan, the proper contents of the house drains are vastly diluted with water, whilst the solid excrement chiefly lodges in the sewers, and has to be carted away from time to time, or is washed into the rivers by a heavy rain.
As regards water supply, it is desirable that all the shallow pump-wells, situated in towns and among houses, should be closed from domestic use, as they are extremely liable to be polluted, and that, as rivers can never be entirely free from pollution, the supply of towns should be from springs or wells at a distance.
In detached houses in the country, where well-water must be used, the wells should not be sunk close to the house, but at a distance; and the water should be conveyed to a cistern in the house by pumping it through a pipe, or in some other suitable manner.
As regards the great question of the purification of the Thames, I believe the part of the river which most concerns the public health is that in the neighbourhood of Thames Ditton and Hampton. I consider that the river in London was never in a better state, regarding it in a sanitary point of view. Not a single water company now obtains a supply from it, hardly any of the inhabitants on the banks dip a pail into it, and I believe the water is much less used among the sailors and others on board ship than formerly. I look on the question of diverting the sewage of London from the Thames rather as a question of taste than a sanitary question; and I shall not attempt to decide whether the improvement in the appearance of the river would be worth the cost. I only hope that, if the measure is carried out, the pump-wells along the course of the operations will be closed, to prevent such a prevalence of epidemic disease as occurred at Croydon; and that if the river is made to look comparatively clean the population will not again resort to drinking the water. If the sewage of London can be conveyed all, or part of, the way to the sea without polluting the river, it is evident that the sewage of Oxford, Windsor, Reading, and other inland towns, cannot be dealt with in a similar manner. The great sewage difficulty arose out of the almost general adoption of water-closets, and I believe it will continue until they are very much diminished in number.
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