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141
The "hardness" of water represents the weight of carbonate of lime, or its
equivalent of other soap-destroying substances, found in 100,000 parts
of water. The average hardness of the Thames water delivered in
London last year, was 180.7; of the Kent Company's water 27°.9; and
of the Colne Valley Company's water 4°.8 only. The difference in
hardness which the waters exhibit is of no importance when they are
used for drinking; but when used for the production of steam, or manufacturing
or laundry purposes, the advantages of soft water, such as
furnished by the Colne Valley Company, are very great. In the
washing of linen soft water is indispensable, and if water is not
delivered soft it must be softened by addition of carbonate of soda, or
by means of soap which is more costly. When water is softened in
detail by the laundress, the operation costs, for an equal volume of
water, about eighty times as much as it costs when conducted on a
large scale by a water company. The only water well fitted for
washing, delivered in London during the past year, was that of the
Colne Valley Company, which, naturally hard, being drawn from the
chalk, is artificially softened before distribution.
All waters, save artificially prepared distilled water, contain more or less
"solid matter." A large proportion of this solid matter consists of
mineral salts which "harden" the water but do not impair its quality
for drinking.
The deep-well waters delivered by the Kent Company and by the Tottenham
Board of Health, contained the largest proportions of solid matter; but
the deep-well water derived from the same source, as supplied by the
Colne Valley Company, contained little more than one-fourth of the
quantity found in the river waters, and less than one fifth of that in
the Kent Company's water. This comparative freedom from saline
matters is attained by adding a small quantity of slaked lime to
the water (Clark's process) before it leaves the Company's works.
The water supplied to the Metropolis generally would be improved by
being submitted to the same process or one of its modifications.
Owing to the careful filtration to which river water is now subjected,
to the improved means of storage at the command of the
Companies, it being no longer necessary to impound the worst flood
waters, and to the action of the Conservators, the average quality of
the water supplied has become better, year by year, and more uniform
throughout the year. Deep-well waters undergo such a prolonged,
exhaustive and inimitable natural filtration through great thicknesses
of porous strata, as to render it extremely unlikely that any suspended
organic matter known to be prejudicial to health should have escaped
removal. Hence these waters are "uniformly bright, pure and
wholesome."
The following table exhibits the proportional amounts of organic elements
(organic carbon and organic nitrogen) in the waters of the Companies