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"The average proportion of organic matter in the waters supplied by the
(local) Companies is thus seen to be identical, but much more uniformity
is observable in the case of the water of the Chelsea and West Middlesex
Companies, which are provided with extensive storage reservoirs, than in
the case of the Grand Junction Company, who in consequence of the
very limited storage capacity they possess are less independent of floods
in the river. This Company has, however, within the last few years
constructed very important works, by means of which much of the
water which they obtain is subjected to natural filtration in the gravel
beds adjoining the Thames, and it is doubtless in consequence of this
improved method of filtration that they have been enabled to supply
water of perfectly clear appearance even when the river was in a very
impure and flooded state." It may be added that the maximum amount
of organic matter in the Thames-derived waters was less than in any previous
year, excepting 1884 only. This greater freedom from an excessive
proportion of organic matter results from the protective measures
which have from time to time been adopted by the water Companies.
The amount of "combined nitrogen," Dr. Frankland stated in a previous
report, "constitutes the whole evidence exhibited by the various waters,
of the nitrogenous organic substances which they have in the past
received, as well as of those which they still retained at the time when the
analyses were made. In river waters the quantity of this total combined
nitrogen undergoes considerable reduction during the warmer months,
owing to the presence of active vegetable life in these waters, under
favourable conditions of temperature.
It was stated in a former report that several of the Companies are now impressed
with the necessity of ultimately abandoning the rivers Thames
and Lea as sources of water-supply, and some of them have already completed
works for utilizing underground waters which have undergone
natural filtration through great thicknesses of gravel and sand, whilst
others are sinking deep-wells in the chalk. In 1884 it had to be remarked
that the protection provided by the common law to rivers was
denied to subterranean sources of water, which, it appeared, as the result
of a decision by Mr. Justice Pearson in an important case (Ballard v.
G