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12
Bacteriological' examinations of the untreated water showed
that, under normal conditions, the wells produce a water of remarkable
purity. Only at times of serious flooding by the river Thames
is a temporary deterioration sometimes observed. Under the present
arrangements this can readily be dealt with by shutting down the
wells concerned for a few days.
There have been complaints that the water tastes of chlorine.
Every effort is made to reduce this to a mininium but this nuisance
cannot be entirely eliminated unless new and very expensive apparatus
is installed.
Fortunately the proportion of residents who are unduly
sensitive to the taste is not large and I am able to say, with confidence,
that the small quantity of chlorine is quite harmless and that
the water supply is wholesome in every respect.
Richmond water contains 30 parts per 100,000 of hardness and
is not plumbo-solvent.
(b) The supply of the Metropolitan Water Board is received
in bulk through six connections off the 30 inch M.W.B. main.
The source of the water is the River Thames abstracted at the
Wraysbury, Walton and Laleham intakes and stored in the Thames
Valley reservoirs at Staines, Littleton and Walton. After storage
the water is treated at the filtration works at Hampton.
The water is filtered by means of primary or rapid filtration
followed by secondary or slow sand filtration. All the water is
finally chlorinated before it leaves the works. In order to provide
adequate contact to ensure complete action by the chlorine a contact
tank is provided at the works which first came into operation in
July, 1948. The water is treated by a method of controlled superchlorination
by maintaining a fixed residual of free chlorine after a
given period of contact.
Samples of water are collected at all stages of the purification
process at least five times each week and analysed at the laboratories
of the Metropolitan Water Board.
Chemical examination was carried out on 244 samples and 817
samples were examined bacteriologically. The results of these
examinations indicated that a very high standard of chemical and
bacteriological purity was maintained throughout the year.