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214
for distribution." Tlie effectual filtration of river water depends,
he says, upon—
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 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 facditated by previous subsidence. The average
rate of filtration, per square foot of filtering area per hour, by the
local companies, in gallons, is, West Middlesex, li; Grand Junction
and Chelsea, If; 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, 1ft.; gravel screened
to different sizes, and arranged in layers, 2ft. 3in. Total thickness, 5£ft
Grand Junction.— Harwich sand, 2ft. 6in.; Hoggin, 6in.; fine gravel, 9in. :
coarse gravel, 9in.; boulders, 1ft. Total thickness, 5½ft.
Chelsea.—Thames sand, 3ft. 3in.; shells, &c., 3in.; gravel, 4ft. 6in. Total
thickness, 8ft.
It avails little, however, that the water is well filtered if it
is allowed, as so frequently happens, to deteriorate in the cisterns
of the consumers through the uncleanly condition of those
receptacles, and the connection of them with the drains through
the medium of " waste-pipes," which the Companies only have
the power to abolish under the provisions of the 14th water
regulation, which reads as follows:
Regulation 14.—"No over-flow or waste-pipe, other than a warning-pipe,
shall be attached to any cistern supplied with water by the Company,
and every such overflow or waste-pipe existing at the time when these
Regulations come into operation shall be removed, or at the option of the
consumer shall be converted into an efficient 'warning-pipe,' within two