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"that the filtered water of the Thames and Lea is unimpeachable
in respect of its wholesomeness and suitability for town
supply," and they are evidently of the same opinion still.
Colonel Bolton's Report.—I now turn to the Annual
Report of Colonel Bolton, the Water Examiner appointed
under the Act of 1871, in which are embraced many paiticulars
of general interest relating to the water supply.
Colonel Bolton, it should be mentioned, makes monthly
examinations of the various waterworks, and in monthly reports
duly sets out the results of such examinations. One of the
most important of his duties is to ascertain whether or not the
requirements of Section 4 of the Act of 1852 are complied
with, viz., that "every Company shall effectually filter all
water supplied by them within the metropolis before the same
shall pass into the pipes for distribution." The effectual filtration
of river water depends, he says, upou —
1. A sufficient area of properly constructed filter beds, constantly clean,
and fresh sanded from time to time as the original thickness is
reduced.
2. The rate of filtration being controlled and limited to a certain speed.
3. The water delivered into the filter beds having been previously stored in
subsiding reservoirs, and the capacity of these reservoirs being such as
to avoid the necessity for the intake of turbid and muddy water during
the time of extraordinary and heavy floods, which tend to foul and
choke the filters.
The rate of filtration should not exceed 540 gallons
per square yard of filter bed each 24 hours, or 2½ gallons
per square foot per hour, and no Company now exceeds
this rate, which, for all practical purposes, may be considered
as a standard. The means of storage for subsidence, and the
area of filter beds, possessed by the several local Companies,
appear to be now adequate to secure effectual filtration as required
by the Act.
The filters of the several local companies are formed as
follows:—