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ham, and the Head Teachers of the Schools ; Matrons and Staffs of Day
Nurseries ; and of Private Maternity Hospitals for their co-operation.
The Medical Practitioners in the Borough were extremely helpful and
thanks are expressed to them for the many voluntary notifications received.
I am indebted to the many traders engaged in the sale or distribution of
food who permitted their premises to be used in the investigations ; and to the
district inspectors for the able manner in which they carried out the extra
work.
WATER SUPPLY.
We are so accustomed to expect a pure water supply from our taps that
we sometimes forget the necessity for constant supervision of the supply. I
am indebted to Lt.-Col. E. F. W. Mackenzie, Director of Water Examination,
Metropolitan Water Board, for the following report:—
" The water supply to the Twickenham area is abstracted from the
River Thames at Laleham and Walton, purified in the storage reservoirs at
Littleton and Walton and at the filtration works at Hampton.
All the water is chlorinated before it leaves the works and adequate
contact to ensure complete action by the chlorine has been provided at
Hampton by the building of a contact tank which first came into operation in
July 1948. The dose of chlorine required to achieve satisfactory sterilisation
is governed by the maintenance of a predetermined residual of free chlorine
after a certain period of contact. This figure is checked at frequent intervals
by the Chlorination Attendants, the dose of chlorine being adjusted accordingly,
and, in addition, an instrument is in operation at Hampton which records
continuously on a chart the residual chlorine in the water after a given period
of contact.
The new method of treatment has been in operation for more than a year
and it is now possible to assess the results of this method of controlled superchlorination.
Taking as the highest standard of bacterial safety of a water
the absence of Bacterium coli in 100 millilitres of sample, it is found that the
percentage of samples drawn at Hampton works which did not comply with
this standard in 1946 (when the ammonia-chlorine process was in use) was
2.5, whereas in 1949 this figure had fallen to 0.3. It has also been found that
the amount of colouring matter in the water pumped into supply fell from
19 units in 1946 to 14 units in 1949, a reduction of over 25 per cent.
All new and repaired mains are disinfected with chlorine before being
restored to supply and samples of water from them are tested bacteriologically.
None of the supplies is plumbo-solvent.
Samples of the water are collected at all stages of purification at least
five times each week and are analysed at the laboratories of the Metropolitan
Water Board. The results are shown in table No. 9."
Number of houses supplied by the Board :—
(a) Direct 29,767 (106,883 persons)
(b) By means of standpipes 9 (17 persons).
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