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98
the water is subjected before distribution; yet, in spite of
these protective measures, there is no absolute guarantee
that these noxious ingredients, which may at any time be
present are wholly removed.
From his observations on the numbers of microbe
colonics developed in samples of the Thames water and
the filtered product, he draws these among other conclusions:—
That bacterially as well as chemically, filtration or percolation
is immensely more efficient for the purification of water than
mere flow for scores of miles in a river.
"That it is possible, by careful filtration, so to arrest
microbes and their spores, as to transform Thames water into a
beverage which, bacterially, is but little inferior to that from
deep wells in the chalk."
The subjoined Table shows the average result of the 12
monthly analyses of water from the Thames at the intakes
and as delivered by the two companies, and the last
column gives the number of microbe colonies in each cubic
centimetre of the raw water and the water as it leaves the
filter beds:—