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(2) Filtration. The water is passed through beds of gravel
and sand and this process removes impurities. Formerly filter
beds were in use at Petersham, but as it was found that the water
was not improved out was not in such good condition as before the
filtration, it was decided to give up this method of treatment.
(3) Chlorination. This method of treating the water is in use
in connection with our water supply. It is used by many Water
Authorities all over the country including the Metropolitan Water
Board. It is not a new method, having been in use in some
districts since 1910.
During the War the system was introduced into the Army and
water known to be seriously polluted was drunk by the troops after
having been chlorinated by the addition of chlorinated lime
(containing a percentage of free chlorine).
In our Supply the Chlorine is introduced as a gas by means of
special machines which work automatically.
There are machines at one of the Petersham Wells, one of the
Old Deer Park Wells and at both Ham Wells.
The water from the first two of the above is mixed with the
water from the other Petersham Well, the other Old Deer Park
Well and the Deep Well.
These machines are very reliable and can be set to give out a
certain amount of Chlorine to any given quantity of water. They
are examined at least twice every day and if one should fail to
function, the other machine would be emitting enough chlorine to
keep the water in a satisfactory condition.
It is most unlikely that both machines would fail at the same
time. In the event of a stoppage of a Chlorinating machine for
some time, the pumping from that well is stopped.
Only a small quantity of chlorine is required to be added to
the water. At present, one part of chlorine is added to four