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205
flushed out and refilled; samples of water are then collected
from these treated mains; and the mains are returned to
service only after results are found to be satisfactory.
The quality control from these laboratories is carried out
by means of daily sampling from sources of supply, from
the treatment works or well stations, from the distribution
system, and through to the consumer. Any sign of contamination or other abnormality is immediately investigated.
(c) (i) The Board has no record of the number of structurally
separate dwellings supplied in your area, but the population supplied direct according to the Registrar-General's
estimates at 30th June, 1967, was 231,150.
(ii) No houses were permanently supplied by standpipe.
(d) No fluoride was added, and where the fluoride content is
indicated in the analyses it represents the naturally
occurring fluoride in the water.
(2) (a) The supply was derived from the following works and
pumping stations:—
River Thames from Hampton and Surbiton via Deptford;
Deptford, Wilmington, Darenth, Bexley, Wansunt and
Crayford Wells.
No new sources of supply were instituted and there were
no changes to the general scheme of supply in your area.
The number of samples collected and the bacteriological
and chemical analyses of the supply from the above
sources after treatment are shown on the attached sheets.
(b) The Board's river and well sources have not been considered to have a plumbo-solvent action, on account of
their hardness content and alkaline reaction. It should,
however, be appreciated that all types of water pick up
varying amounts of metal from piping, particularly when
it is newly installed; this applies to copper, zinc, iron and
also lead.
Tests for lead have been carried out in connection with
chemical analyses of samples of running water collected
from premises in the distribution system and I set out
below the information obtained over the period 1st
January to 31st December, 1967