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supplied by the Colne Valley Company contained less than one-half
the quantity found in the river waters, and less than one-third of that
found in the Kent and Tottenham waters: this comparative freedom
from saline matters being attained, as already explained, by adding
a small quantity of slaked lime to the water before it leaves the
Company's works. The process is equally applicable to all waters
supplied to the Metropolis.
The organic impurities derive their importance from being of animal
origin. They are found in the river waters, which last year were
often much polluted, so that, even after efficient filtration, Dr.
Frankland deemed them only in some measure fit for dietetic
purposes during the months of April, November, and December."
Only once before, since 1868, when these analyses were first made, had
the Thames water been so polluted as in 1879; and, but for the perfection
of the Companies' filtering plant, there is reason to believe that
the pollution of Thames water, as delivered in London last year,
would have been unprecedented. "The Thames was often in high
flood, even in summer, and much filthy matter from sewers, cesspools,
and cultivated fields was swept into the river during those periods of
the year when they are usually kept back by the absence of heavy
rain" The Lea water was somewhat superior; but in several months
that sent out by the East London Company was "quite unfit" for
dietetic use. These "noxious organic matters" are "in suspension,"
but in such a finely divided state as to render their removal by
artificial sand filtration impossible. There is thus no protection against
the distribution of them in polluted river water. Deep-well water, on
the other hand, has undergone such a prolonged and exhaustive
filtration through great thicknesses of porous rock, as to render it
extremely unlikely, if not impossible, that any portion of the organic
matter still remaining in it should be of this noxious character."
Hence the deep-well waters were "uniformly pure and wholesome."
Of the river water abstracted from the Thames, the best average
supplies were furnished by the Lambeth and Chelsea Companies. Not
many years ago the supply by the Chelsea Company was one of the
worst, owing to the unsatisfactory position of their intake—at Seething
Wells—and to deficiency of storage reservoirs. Stimulated by the
complaints of their customers the Company removed their intake to
West Molesey, undertaking extensive works at a large outlay, and now