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gallons. One of this Borough's two wells which supply drinking
water is a prolific contributor to the Board's supplies, having a
normal output of 5 million gallons per day.
The Board is responsible for the purity of its water and the
supplies are regularly tested—chemically and physically for an
estimation of its clarity, colour and taste, and bacteriologically for
assessment of coliform colonies with confirmatory examination for
Escherichia coli.
Water resources throughout the world remain constant whereas
demands for its use are increasing. All water comes from the sea
to which it ultimately returns and this cycle is continuous. Local
cycles concern water evaporation from the land which, together
with that given off by plants in transpiration (a cabbage gives
off one litre of water each day and a tree about 200 litres),
returns to earth as rainfall. In its natural state water is not
separate at different levels but both rainwater and irrigation
water percolate into the ground where eventually, as underground
water, it shares in the general cycle by flowing into rivers,
lakes or even directly into the sea. It follows that pollution of
ground water leads, inevitably, to pollution of water everywhere.
Most of the earth's water is salt (98%) and almost the whole of
the remainder (2%) forms the polar ice caps and is therefore
inaccessible for human purposes. This leaves only the surface,
ground and atmospheric water at our disposal—equivalent to less
than 0.04% of the total.
In these islands water is commonplace and its cost is almost
negligible yet, as a usable commodity, it is not inexhaustible. A
pure domestic water supply in urban areas has become progressively
more difficult to maintain.
Greater London is unique in that it is practically wholly
developed. Over the years, buildings and drainage have disturbed
the natural flow of water and such resources as were available
have been rendered useless for the supply of pure water. Deficiencies
in overground supplies within the county are met by tapping
outside sources which, together with water from the higher
reaches of the Thames and the Lea and the exploitation of the
underground water-bearing strata, form the bulk of London's
supplies. In fact, for some considerable time now, water from
springs, streams and wells has been dwindling and greater use
has had to be made of the Thames which now contributes more