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Annual Report of the Medical Officer of Health,—1893. 35
Briefly, Koch's rules are:—(1) The maximum rate of filtration should not exceed
1.1 or 2.1 gallons per hour, per square foot of filter surface; (2) A separate
bacterioscopic examination of the water issuing from each filtering basin should be
made daily; (3) Filtered water containing more than 100 living micro-organisms in
a cubic centimetre should not be allowed to reach the pure water reservoir. In other
words, such water is unfitted for domestic use.
Professor Frankland states that his bacterioscopic examinations were made
monthly. Professor Koch, advises a daily examination, and holds that a weekly
examination is in all circumstances to be looked upon as insufficient.
Dr. Frankland's tables show the Southwark and Vauxhall Companies' water to
be less pure, bacterially, than that of any of the eight metropolitan water companies.
Its maximum number of microbes, per c.c., numbered as many as 1,220, 134, 566, and
180, in the months of January May, October, and December respectively.
The Lambeth Companies water yielded a maximum of 366 and 202 microbes per
c.c. in January and December respectively.
Its average rate of filtration, per square foot, per hour, was 2.4 gallons. This
figure, which represents the "mean," be it observed, exceeds Professor Koch's
" maximum" of 2.1 gallons.
According to the report of Major-general Scott for 1892, the maximum monthly
rate of filtration per square foot, per hour, of the Southwark and Vauxhall Company,
was 3'50 gallons.
The Eoyal Commission, appointed to inquire into the water supply of the
metropolis, have lately reported, among other matters, that they find the water, as
at present supplied, to be of a high standard of excellence and purity. They also
consider that it can be used without danger, provided there is adequate storage and
efficient filtration.
Notwithstanding this finding of the Commission, the principle involved in first
accepting the sewage-polluted water, and then asking commercial companies to filter
it efficiently, without fixing any standard, does not commend itself to my mind.
Sir George Buchanan, in his evidence before the Commission, hit the mark when
he said he was of opinion that " contaminated waters do, under certain unknown
conditions, produce disease, the cause of which cannot be detected either by chemical,
microscopical, or bacteriological examination. The only really reasonable course to
adopt, therefore, when a water is known to be polluted, as the Thames is, was to
avoid its use."
Should it be eventually proved that the decision of the Commissioners was
arrived at in consequence of incomplete or defective evidence, it will be necessary to
substitute water drawn from a pure deep well or lake, in place of the existing
polluted supply.