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out by the Medical Officer, who was assisted in this particular
work by Dr. L. Rajchman, of the London Hospital University
College. The full account of the investigation is too detailed to be
inserted here, but the following summarised report was made to
the Council:-
16th February, 1914.
I beg to submit the following report on the bacterial purification
of the water supply of Croydon and the experimental enquiry recently
carried out on the chlorine method of the bacterial purification of
water.
The scientific fact underlying the chlorine method of water purification
is that free uncombined chlorine kills bacteria. The aim of the
enquiry was
(a) To test the practical efficiency of the chlorine treatment of
water and
(b) To determine the best practicable means of removing the
chlorine from the water before distribution.
(a) Chlorine Treatment.—Throughout the experiments the chlorine
was added to the extent of one part of chlorine to one million parts of
water or one-half part per million, as was desired. In every instance
the water treated was previously charged with bacteria to an extent
far beyond that which could ever occur in an ordinary water supply.
The contamination took the form of pure cultures of intestinal bacteria,
spore-bearing bacteria (the most resistant form of bacterial life), urine
containing bacteria, water charged with human excreta, and surface
road washings. The results of the experiments were in all cases highly
satisfactory—the treatment by chlorine invariably destroyed all the
organisms, the water at the end of the process being found to be
bacteria-free.
(b) Chlorine Removal.—The second stage of each experiment was
an enquiry into the means of removal of the chlorine from the water
before general distribution. Three methods were advocated, viz., the
addition of an alumina compound to the water, or the addition of
sodium hyposulphite to the water, or the filtration of the water through
a layer of charcoal. The two methods first named are absolutely
ineffective. The filtration through charcoal, on the other hand, has
been entirely successful.
It has appeared desirable to compare the results of this enquiry
with those obtained by Prof. Hewlitt and Dr. Nankivell in the investigation
carried out in Croydon by them a few years since into a combined
process of water softening and bacterial purification. The bacteriological
results obtained in this enquiry are markedly superior to
those obtained by Drs. Hewlitt and Nankivell, and as all the tests
applied were of the most searching nature, I unhesitatingly affirm that
the chlorine method of treatment is the more efficient bacteriologically.
In my opinion the chlorine method of water purification is a
thoroughly efficient one, and may safely be used by the County Borough
Authority for the treatment and purification of the Croydon water
supply.