Let me likewise take the opportunity of correcting a misapprehension, which, by the use of an inappropriate word, is sometimes shown to exist on this subject. The agents in question are spoken of as dis-infectant. As there is no scientific reason whatever for believing that they in any degree interfere with the spread of epidemic or infectious disease, and as an erroneous opinion on this point may lead to the neglect of measures which are truly precautionary and useful, I think it well to state explicitly, for your information, that I have no evidence of their possessing any other utility, in the respects under consideration, than simply and singly that of removing stink from the atmosphere around them.
For reducing to a minimum the exhalations which arise from sewers and house-drains, it appears to me that the following are the essential principles: First, to render the current through them as rapid as possible; and, above all, by every care for their form, their junctions, their slope, and their material, to provide against the occurrence of obstructions and deposit: Secondly, to employ in their construction, so far as may be possible, such substances as are porous in the least procurable degree; such as consequently will be least apt to imbibe and retain in their interstices any considerable impregnation from the fœtid fluids running over them at intervals; such, too, as will be least likely to permit soakage into the surrounding soil: Thirdly, by reducing the size of drains and sewers to the lowest dimensions compatible with a full performance of their uses, to diminish to the utmost the extent of their interior evaporating surface, and of those large chambers which they now offer for the evolution, retention, and diffusion of gases.
To the application of these principles (together with a sufficient and appropriate distribution of water) far more than to chemical agents, or to the invention of mechanical traps, I believe that you must look for rendering inodorous the vicinity of your numerous gully-holes. I content myself with stating them to you, as a practical deduction from physical laws, without venturing to offer any opinion on the degree in which they are applicable within your jurisdiction, or on the manner in which they should be applied. For although, as principles, they have their foundation in physics, and although their importance to sanitary improvement is beyond measure great, all details relating to their application lie out of my province, and belong to a class of subjects in which your Surveyor’s opinion will, of course, be infinitely more useful to you than mine.
Water-Supply.
During the past year, as in the preceding one, I have given frequent consideration to the subject of water-supply within the City.
I have already endeavoured to convey to you the deep sense which I entertain of its importance, and I have every reason to believe that your Hon. Court recognises, at its full weight, the necessity of providing for the City of London a supply of water which in quantity shall be ample, in quality pure, in distribution constant and accessible.
In my [former Annual Report], and in some remarks subsequently addressed to your Committee of Health, I dwelt especially on such defects of our present system as relate to the quantity and distribution of water; endeavouring to illustrate the insufficiency of its supply to the poorer tenements of the City, and the extreme inconvenience which is entailed on their inmates, sometimes by dependence on a common tap, sometimes by the troublesome, expensive, and unwholesome necessity of storing water.
In reverting to this subject, I may correct a fallacy which is apt to prevail with respect to the abundance of supply. I have no reason whatever to doubt that a very liberal allowance of water is daily pumped into the City—enough, or more than enough, so far as I know, to fulfil all necessary purposes.
But those purposes are not fulfilled by it. A certain large figure is stated as representing the average quantity daily driven through the mains of the City; this quantity is divided by the number of residents within your area, and the inference is drawn that each individual inmate of the City has at his disposal 25 gallons a day; or (after deduction for public purposes and the like) 211⁄4 for his domestic supply. As an arithmetical conclusion from the premises this may be true: nothing can be less accurate as a practical representation of the facts. An average amount of three million gallons per diem may, or may not, be pumped through the mains of the City: but to calculate the available water-supply from this dividend, without previous deduction for the immense escape of un-available water by waste-pipes or otherwise, gives a most fictitious result. The large waste which naturally arises in the system of intermittent supply has been well illustrated by some evidence given by Mr. Lovick before the late Metropolitan Commission of Sewers, in respect of a particular block of nearly 1200 houses.[47] Some of the houses were of the higher, and many of the poorer class, but the average might be stated to be of the middle class, and to present a fair example of an urban population. The drainage of all these houses was discharged through one main sewer. The run of water through this sewer was carefully watched and gauged every hour, during the night as well as the day, on days when the water was on, that is to say, when the intermittent supplies were delivered, and also on the ordinary days, when the consumption of the houses was from butts and cisterns, into which the intermittent supplies were delivered. The gaugings of the discharge of waste water into the sewer were checked by gaugings of the consumption of water from the butts and cisterns, during the interval of the delivery of the supply by the company. It was ascertained that the average quantity discharged per diem through the sewers was 441⁄2 gallons per house; but it appeared that, on the days when the intermittent supplies of water were on, the quantity discharged per diem was 209 gallons per house. The waste in this district from defects in house apparatus of distribution, incident to an intermittent supply of water, was, on the water days, three and three quarter times greater than the consumption on those days.
[47] General Board of Health Report on Supply of Water to the Metropolis, page 120.