View report page

243
This water thus remains cool and refreshing in summer, and is less
likely to become frozen in the service pipes in winter.
The solid matters found in the waters are mostly composed of mineral
substances which, in existing proportions, in no way diminish their
fitness for drinking. But the salts of lime and magnesia, which constitute
the principal part of these mineral ingredients, are objectionable,
imparting to the water its "hardness." The small proportion
of organic material which the solid matter contains is of the greatest
importance in connexion with the use of water for drinking purposes,
as it may be of the most objectionable character on account of its
origin. Thus the Thames receives, above the Metropolitan Companies
intakes, various contributions of organic matter of animal origin, such
as the drainage from manured land, the effluents from sewage works,
and even sewage itself. This animal matter may, at any time, be
accompanied by zymotic poisons dangerous to health, and although
the chance of such substances reaching the water consumer are greatly
reduced, both by exclusion of flood waters from the reservoirs and by
filtration, there is no absolute guarantee that the noxious ingredients,
which may at any time be present, are wholly removed. The deep
well water from the chalk contains much more solid matter than the
river waters. But the Colne Valley Company, by treating this chalkwater
with lime, reduce the solid matter to little more than half the
quantity present in river water.
During the greater part of the year the river waters contained only a very
moderate amount of organic matter—a smaller average indeed than in
any previous year since 1868, when these determinations were first
commenced. The well known purity of the chalk-water was maintained,
the average proportion of organic matter which it contained
being but little more than one-third of that present in the Thames.
From a sanitary point of view, moreover, the superiority of deep well
water is even greater than the figures represent, for the exhaustive
filtration it undergoes, in passing through a great depth of porous
strata, is far in excess of what can be effected by sand filtration. The
greater the storage capacity possessed by any company the more independent
it becomes of floods in the river, and the less proportion of
organic matter will be found in its water.
The whole evidence of the nitrogenous organic matters which have gained
access to river waters in the past, as well as those which are still present
at the time of analysis, is furnished by the total amount of combined
nitrogen both mineral and organic. In river water this total
combined nitrogen undergoes considerable reduction in summer, in