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143
of organic impurity present in the waters taken from
the Thames, the Lea, and the deep wells respectively,
from 1868 to 1888. From the figures there given, it
will be seen that the Thames water supplied during
the past year was, in respect of comparative freedom
from organic impurity, only surpassed in two out of
twenty-one years, that there was in the Lea Water a
general freedom from organic matter, but that the
highest degree of purity was shown last year as in
former years by the deep well water, the average proportion
of organic matter contained in it being but little
more than one third of that present in the Thames,
and slightly more than one half of that in the Lea
water. It must be borne in mind also, that from a
sanitary point of view, the superiority of this deep
well water is not fully represented by a comparison of
the analytical figures, for the exhaustive filtration
which the deep well water undergoes in passing through
a great depth of porous strata is far in excess of what
can be effected by the sand filtration, highly valuable
as it is to which the river waters are subjected.
Table B shows the maximum, minimum and average
proportions of organic impurity in each of the waters,
the average amount contained in the Kent Company s
water during the nine years ending December, 1876,
being taken as unity.
It appears from this table, that of the deep well
waters, that supplied by the Kent Company contained