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during the last 80 years has proved injurious to the consumer, it does not appear to me that this
experience, satisfactory as it is so far as it goes, justifies the assumption that there is a complete absence
of risk in the use of water from the London rivers. In attempting to estimate the value of this 30
years' experience, it is necessary to have regard to the opportunities which have existed during this
period for ascertaining whether injury has resulted, and these opportunities, while perhaps sufficient for
the purpose of showing a large or conspicuous injury, would not have sufficed for the demonstration of
smaller injury, such as might possibly occur from the use of water from these rivers. Under any
circumstances the investigation of the subject is full of difficulty, but the difficulties have been increased
by the absence of any sufficient machinery of observation. An increase in the number of cases of enteric
fever in London, such as would be likely to result from the supply of imperfectly filtered flood water,
might, under such circumstances, readily occur without suspicion attaching to the water supply.
For such purpose a system of notification of cases of infectious disease was necessary, and this system
has only existed in London during the last few years, and again, an organisation was necessary which
would have provided for a proper study of the behaviour of enteric fever in connection with the circumstances
of the water supplies, and such organisation did not exist.
I think regard must be had for the absence of this very necessary machinery in any conclusion
which is based on the experience of the last 30 years. But beyond this it must not be forgotten that
circumstances which would now be held to raise question as to the wholesomeness of a water supply,
would not in the past have created any suspicion. Indeed, the difficulty of obtaining recognition
of the value of such evidence as can be adduced in connection with water-borne disease,
even at the present time, cannot be better exemplified than by reference to the unwillingness
of the Royal Commission to accept as conclusive the evidence Dr. Barry was able to submit as to
enteric fever in the Tees valley, evidence of which the medical officer of the Local Government Board
writes—" Seldom, if ever, has the proof of the relation of the use of water so befouled to wholesale
occurrence of enteric fever been more obvious and patent."*
The favourable opinion entertained by the Royal Commission as to the quality of the water
supplied to London is, moreover, dependent on the provision of adequate storage and efficient filtration,
and with regard to existing arrangements the Royal Commission reports—" We cannot shut our eyes
to the fact that the provision for this purpose differs enormously in the different companies, and in
some of them is to our mind quite inadequate." In the report mentioned I have referred to
the uncertainty attaching to the action of filter beds; in this connection I may cite the opinion of
Professor Koch, of Berlin, who thus writes in 1893—" All that we know of sand filtration therefore
compels us to admit that, even under the most favourable circumstances, it cannot afford absolute
protection against infection, though, as I have already said, it does afford a protection with which,
considering the practical conditions of life, we may rest content."!
Dr. Frankland, reporting to the President of the Local Government Board on the chemical,
physical, and bacterioscopic examination of the waters supplied by the metropolitan water companies
during the year 1893, points out the need of sufficient storage to tide over the largest floods, or of the
means of substituting the river water for stored water whenever the chemical quality of the former is
better than that of the latter. Thus, he points out, the impounded flood water affected the quality of
the supply in March, making it in that month of worse quality, from a chemical point of view, than the
raw river water passing the companies' works at the same time. His report is accompanied by
diagrams, one of which compares the organic impurity of the raw Thames water at Hampton with that
of the average filtered water delivered in London by the five companies drawing from this river, and
he states that " except in February and March, the diagram shows that the water delivered by the
Thames companies in London was of excellent chemical quality, and it also shows that the lesser flood
of October was successfully excluded." Another diagram compares the raw Lea water at Angel-road
with the filtered supply of the East London Company as delivered in London, and he states that this
diagram shows that even 15 days storage was not sufficient to circumvent the long flood of February.
He points out that " in that month the stored water was of inferior chemical quality to that of the Lea
passing the intake, and this condition of things was even more marked in the following month of
March, when the organic impurity in the stored water was represented by the figures 4"2, whilst that
of the raw Lea water passing the company's intake was represented by 2'4 only. During the remaining
months of the year this company's water was, as the diagram shows, of excellent chemical quality.
The excessive impurity in the raw water in June was completely excluded from the supply, but the
flood water of October was not quite so successfully dealt with as was the case with the Thames water
in that month." A diagram contrasting the organic elements contained in the unfiltered water of the
New River cut with the amount present in the supply of the New River Company shows, Dr. Frankland
says, that " except in March, when doubtless owing to recent floods in the Lea the New River Company's
supply contained an exceptionally large proportion of organic matter the quality of this
company's water was uniformly excellent, and in some cases even better than the average of the deepwell
waters."

* Supplement to the twenty-first annual report of the medical officer of the Local Government Board
f Zeitschrift fiir Hygiene und Infectionskrankheiten.
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