View report page

192
capacity of the reservoirs for unfiltered water, belonging to
each of the local Companies, was as follows: Chelsea 142,
West Middlesex 7, Grand Junction 3.5. The East London
Company is the only one that possesses larger capacity than
the West Middlesex, viz., 13.7 days. supply, thus coming second
to the Chelsea Company. But the Grand Junction Company
have the means, during floods, of pumping from the gravel
beds adjoining the Thames, and this is practically equivalent
to an addition to their storage resources.
Provision was made by the Metropolis Water Act, 1,852
(sec. 4), for the efficient filtration of all water supplied by the
Companies before distribution. Testimony is uniform that
this provision is faithfully carried into effect. The late Sir
Francis Bolton, the first Water Examiner appointed under
the later Act (1871), laid down the conditions necessary to secure
this object; viz. (1) Storage in subsidiary reservoirs, of capacity
sufficient to avoid the necessity of intake of flood waters;
(2) A sufficient area of properly constructed filter beds; and
(3) The limitation of filtration to a certain speed, represented
by the passage of about 540 gallons, per square yard
of filtering area, in 24 hours, or 2½ gallons through each square
foot of surface per hour. These conditions are fully complied
with by the several Companies, with the result that, whatever
the condition of the water when taken from the river, or passed
on to the filtering beds, the filtered water is uniformly bright
and clear. Sand is the efficient agent in filtration for securing
brightness and clearness; but microbic separation appears to
be secured by the gelatinous scum, itself mainly microbic in
character, which after a little time forms on the surface of the
sand, and which, until lately, was regarded as an impurity
requiring to be frequently removed. In former reports I have
fully described the apparatus of filtration, and to those reports
I may refer for detailed information on the subject. It need
hardly be said that filtration, however perfect, avails little, if
the water is allowed, as frequently happens, to be fouled in