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199
Company is at West Molesey, the intakes of the other Companies
being at Hampton. The Grand Junction Company is constructing
a new intake, on a small island composed of clean ballast,
about one mile above the intake at present in use: the water
will percolate through the ballast and so enter the conducting
culvert in a clear condition. This Company's supply, moreover,
is supplemented from sand and gravel beds at Hampton, the
Company haviug a complete system of underground collection of
water on about '20 acres of land, and being able, during the time
of flood, to raise large quantities of water that has passed through
the natural beds of gravel and sand, which are characteristic of
the neighbourhood. " The gravel-beds in the Thames Valley "—
we are told by the Water Examiner—" form in some localities a
valuable source of supply, the importance of which is being
recognized; and which, moreover, is probably capable of being
far more largely utilised .... while the integrity of the ground
in respect of pollution is assured " ; for, of course, with the growth
of population, and its nearer approach to such sources of supply,
the risk of sewage-pollution increases; such risk, moreover, arising
in a greater or less degree from the manuring of surface lands.
" This being the case, there exists always the possibility of the
introduction of specific matter of a noxious character."
Owing to the effects of rain, the Thames was in a more or less
indifferent condition during 191 days of the past year. Nevertheless,
the filtration carried out by the Companies was almost uniformly
effective in freeing the water from all traces of turbidity. Turbid
water is very difficult to filter. The solid impurities in suspension,
chiefly consisting of clay, marl, and chalk, in a very finely
divided state, can be got rid of only by long subsidence previous
to filtration. Turbid water must of necessity be sometimes
admitted, and the filters are then overtaxed.
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