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232
It need hardly be said that filtration, however perfect, avails little,
if the water is allowed, as frequently happens, to he fouled in the
cisterns. The attention of householders cannot therefore be too
frequently drawn to the necessity for the periodical cleansing of
cisterns used for storing potable water. Cisterns, moreover, should
be properly covered, so as to exclude light and dirt; and so placed
that the water may be kept cool in summer, without being in danger
of freezing in winter. It may be added that when "constant supply "
is given, a screw-down draw-off tap should be affixed to the rising
main, or service pipe, so that drinking and cooking water may be
drawn therefrom, fresh and uncontaminated, without the intervention
of cisterns, which are required for washing, flushing, baths, and similar
purposes. A stop-valve, moreover, should be fixed outside the
premises to prevent damage to the house, in case of pipes burst
by frost or other causes. But to resume.
The estimated quantity of water for domestic purposes stated to
have been supplied by the Grand Junction, the West Middlesex, and
the Chelsea Companies respectively, in May 1892, averaged 47.5,
30.8, and 36.8 gallons per day, per head of the population; and 323,
233, and 292 gallons per house. But doubts exist in regard to
the accuracy of the statistics—of houses, population, and water—
supplied by some of the companies to the Water Examiner, the subject
being admittedly a difficult and complicated one, so that the estimates
given can only be considered as approximate. The "intake" of
the Chelsea Company is at West Molesey, the intakes of the other
Companies being at Hampton. The Grand Junction Company has
constructed a new intake, on a small island composed of clean ballast,
about one mile above the original intake: the water percolates
through the ballast and so enters the conducting culvert in a clear
condition. This Company's supply, moreover, is supplemented from
sand and gravel beds at Hampton, the Company having 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