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181
Temperature: Although the average temperature
differs but little for the several supplies, the monthly
variation in the case of the river waters is very great,
whilst the temperature of the deep-well water is practically
constant throughout the year. Thus the water
principally derived from the Thames and supplied by
the Chelsea, West Middlesex, Southwark, Grand
Junction, and Lambeth Companies, varied in temperature
from 3 4°.9 Fahr. in January to 68°.5 Fahr. in
July, and the water of the Lea distributed by
the New Kiver and East London Companies fluctuated
from 35.8° Fahr. in January to 65.3° Fahr. in July.
The deep-well water of the Kent Company on the
other hand, was free from these violent fluctuations,
and practically maintained a constant temperature
throughout the year. This uniformity of temperature
of deep-well water is of considerable importance, as
the water remains cool and refreshing in summer and
is less likely to become frozen in the service-pipes in
winter.
The solid matters in the water are almost wholly
composed of mineral substances, which, in the proportion
in which they exist in Metropolitan waters, in
no way diminish the fitness of the water for drinking.
But the salts of lime and magnesia which
constitute the principal part of these mineral
ingredients are objectionable, not only because they
impart to the water what is known as "hardness,"
and thus render it unsuitable for washing, but also