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68
he takes as his standard of purity, and his observations hereon
assume greater importance on the present occasion, considered
in connection with a scheme which has just been propounded
by eminent engineers, under the auspices of the "Water
Authority," (i.e., Metropolitan Board of Works), with the object
of supplying the Metropolis with potable water from this source.
Dr. Frankland reminds us that our water supply is derived
from the Thames, the Lea, the " New River," and the deep
wells in the chalk. The range of temperature of the river
waters is considerable—no less, last year, than 350.5 Fahr ; viz.,
from 33°.8 in January, to 70°.7 in July and August. Thus they
were in danger of freezing in winter ; and they were unpleasantly
vapid and warm in summer. The deep well water, on the other
hand, had a range of only 8°.1 Fahr, viz., from 500. to 58°.1
The amount of solid impurity in the waters is much the same
year by year. It is composed of a variety of substances, most
of them harmless when the water is used for dietetic purposes,
but injurious when used for washing. The really objectionable
part consists of organic matter; and is sometimes dangerous to
health. This is almost, if not quite, exclusively found in river
waters ; and is to a great extent of animal origin. "On the whole
the year, 1876, was very favourable for the river waters. Up to
the end of November the rainfall was greatly below the average,
and in consequence much polluting matter, which would otherwise
have been washed into the rivers, was retained nearer to its source.
Some months the river waters contained much less organic impurity
than usual: indeed in August and October the New
River Water was chemically purer than the deep well water of the
Kent Company. When, however, the heavy rains of December
set in, the accumulated filth of the summer and autumn was
swept into the neighbouring streams, the Thames overflowed
its banks, washing the manure from cultivated land, and liberating
the water from stagnant ponds and ditches. Thus during the
last month of the year, the Thames was laden with organic matters
of the most objectionable origin, which were carried down to the
intakes of the Metropolitan Water Companies : they passed through
the filters, and were distributed to consumers. Since January,
1873, the Thames has never been in such a filthy plight, and
although most of the water companies drawing from this river
have greatly improved their subsidence and filtration plant since
that date, no care, foresight, or appliance could convert the
'puddle' (to quote an entry in the books of the West Middlesex
Company) which entered the Companies' works, into
wholesome potable water fit for dietetic purposes. These uncontrollable
and frequently occurring outbreaks render this river
a very undesirable source of water for domestic use."