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175
The fact that the impurity of the water in the river is so
largely increased during periods of flood, renders it of great
importance that there should be sufficient provision of subsidence
and storage reservoirs to enable the necessary daily supplies to be
delivered during such periods, while keeping the intakes closed.
The position of the several Companies varies in this respect very
considerably. The following statement shows the number of days'
supply, represented by the capacity of the reservoirs for unfiltered
water, belonging to each of the local Companies:—Chelsea 14;
West Middlesex 8 ; Grand Junction 4. It must be mentioned,
however, that the Grand Junction Company's resource, during
floods, of pumping from the gravel beds adjoining the Thames is
practically equivalent to an addition to their provision of storage
reservoirs. For sake of comparison it may be added that the
East London Company has capacity for 16½ days' supply. The
same Company is stated to be conspicuous by its advance in
work for improving the water supply of its district in other
respects.
Dr. Percy Frankland continued in 1886 his biological experiments
by the process known as gelatine-plate cultivation, from
which it appears that the average reduction in the micro-organisms
(bacteria) present in the unfiltered water of the Thames, effected
before delivery to the consumers, amounted to no less than 96.5
per cent, a striking evidence not only of the importance, but also
of the efficiency, of filtration as practised by the several Companies.
The following particulars with respect to the local Companies
may be of interest:—
Storage and Filtration.—No new works have been found necessary by the
Chelsea Company, the existing means being sufficient to meet all
requirements at all times of the year. The West Middlesex Company
have constructed two additional filters at Barnes, of about one acre of
area in each. The Grand Junction Company have connected their
reservoirs at their Kew and Campden Hill Works with the main of the
East London Company, and made connection of mains in other localities,
so that the one Company can assist the other in case of emergency
arising from fracture of a main, etc.