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145
gentleman as "Water Examiner" are multifarious and important.
He makes monthly inspections of the several Metropolitan waterworks,
filter beds, reservoirs, &c.; examines the quality of the
water, both at the intakes and after filtration at the works, and
reports monthly the results of such inspections and examinations
to the Local Government Board. Upon him rests the responsibility
of seeing that the requirements of Section 4 of the Metropolis
Water 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,
upon—
1. A sufficient area of properly constructed filter beds, constantly cleaned,
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. Filtration ought to be effectual at this
rate, which, for all practical purposes, may be considered as a
Standard. Effectual filtration is greatly facilitated by previous
subsidence." The average rate of filtration, per square foot of
filtering area in gallons per hour, for each of the local companies,
is as follows:—West Middlesex, 15/8; Grand Junction and Chelsea,
1¾. The requirements of the Act in this respect, therefore, are
fully carried out.
The filter beds are formed as follows:—
West Middlesex.—Harwich sand, 2ft. 3in.; Barnes sand, lft.; gravel screened
to different sizes, and arranged in layers, 2ft. 3in. Total thickness, 5½ft.
Grand Junction.—Harwich sand, 2ft. Sin.; Hoggin, 6in.; fine gravel, 9in.;
coarse gravel, 9in.; boulders, lft. Total thickness, 5½ft.
Chelsea.—Thames sand, 4ft. 6in.; shells, &c., 3in.; gravel, 3ft. Sin. Total
thickness, 8ft.