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100
No information is available as to the nature
of the micro-organisms to be found in the water from
the filter beds. Table 33 shows the numbers
present in the raw river water and in the filtered
supply. Prof. Frankland adopts as a standard of
pure water, one containing not more than 100
microbes per c.c., and he remarks of the supply of
the West Middlesex Co. that excepting in June and
December, the supply was " of most excellent
bacterial quality, not unfrequently rivalling or
excelling, in this respect, the deep-well water of the
Kent Company " ; and of that of the Grand Junction
Co., " the small amount of storage possessed by this
Company renders it difficult at all times to maintain
efficient bacterial filtration, and 6 out of the 12
samples collected at the Hampton Works during the
year contained an excess of microbes or their spores
over 100 per c.c., whilst 5 out of the 22 samples
collected at the Kew works also contained an
abnormal number."
The West Middlesex Company filter through 275
feet of sand at an average rate of 1"25 gallons per
sq. ft, per hour. On an average 9979 per cent of
the microbes present in the raw river water are
removed by such filtration, ranging from a maximum
of 99.94 to a minimum of 91.48.
A very interesting note is included in the Report
as to the superior efficiency of the finer varieties of