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94
measures will be best indicated by the reduction
effected in the amounts of organic pollution present
in the raw supply, and the number and characters
of the micro-organism present in the purified
water.
When the Thames is in flood, much pollution
(sand, excrement, &c.) is washed into the stream
from the adjacent lands. At such times the water
is unfit to be taken into the supply mains at all, and
therefore the Water Companies having the largest
amount of storage room, are best able to maintain
the purity of their supply. Of all the Metropolitan
Water Companies, the East London has the largest
storage, viz., 15.0 days, that of the West Middlesex
being 5.6, and that of the Grand Junction, 3.3.
During 1896 the West Middlesex Company completed
a series of storage tanks, covering several acres, at
Barnes.
The amount of purification effected by filtration
&c., is indicated in Table 31, which gives the
mean results with the limits of variations during
1896. In Table 32, the mean results for 1896
are compared with those for 1895 and 1894. The most
important element in considering the work of purification
is the extent and frequency of the maxima of
the organic constituents in the water distributed, they
indicating the risks of any untoward chances from the
consumption of impure water.