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239
freezing point." The river water is soft by comparison with the
deep well water, which owes its "hardness" to the much larger
proportion of mineral substances which it contains, and which
compose the great bulk of the "solid matters." The hardness
of the water, sufficiently great to materially diminish its value for
washing, steam, and industrial purposes generally, is almost
entirely due to the presence of bi-carbonate of lime in solution :
this bi-carbonate of lime can be readily removed by treating the
water with lime before delivery, as is so successfully done by the
Colne Valley Company; whereby the hardness of that Company's
water is reduced to about one fourth of its original amount—in
1890 from 29.7° to 7.9°; the hardness of the Thames water
being 20.4°. This mode of softening is by far the most
economical, for it entails only about one-eightieth of the expense
which devolves upon the private consumer in the shape of
additional soap required for washing purposes. The hardness of
the river water is similarly reducible. The small proportion of
organic material which the solid matters contain, is of the greatest
importance in connection with the use of the water for drinking
purposes, as it may be of the most objectionable character, on
account of its origin—such as the drainage from manured land,
the effluents from sewage works, or even raw sewage itself. The
animal matter may at times be accompanied by zymotic poisons
dangerous to health—although the chances of such substances
reaching the consumer are reduced by filtration, and by the
exclusion of flood-waters from the reservoirs. The Companies
are endeavouring to substitute, as far as possible, water from
subterranean sources for raw river water, whilst the Conservators
have almost completely stopped the discharge of untreated town
sewage into the Thames. During the greater part of the year
the water contained only a very moderate amount of organic
matter, the analyses shewing that the Thames water, supplied
in 1889 and 1890, was "superior to that of any former year as
regards comparative freedom from organic impurity." But in this
respect, Thames water is of distinctly inferior quality compared
with the river Lea water. From the sanitary point of view the