cal unit,
measures to satisfy these demands can easily, economically, and quite
logically be designed to furnish a good part of the metropolis'
near-future safe margin of water supply as well.

[Illustration]

A need for vigorous research specifically directed toward exploring all
these alternative means of supply is evident. If it moves fast enough
and the knowledge that comes out of it is made available to planners, it
may very quickly make a great difference in the kinds of sources of
water they can turn to for the solution of problems, just as studies
since the early 1960's, when the Army work on the Potomac was completed,
have altered prevalent ideas about pollution control through flow
augmentation, and have therefore greatly diminished the overall amount
of water considered necessary to meet the Basin's demands.

In the crucial meantime, the established certainty of storage in
reservoirs is available. In river basins with reasonable annual amounts
of precipitation but with human demands on streams that sometimes exceed
the rate at which water flows down, such reservoirs are still usually
the most dependable and efficient item in the present technology of
water supply. And since they generally have other purposes to which
proportionate shares of construction costs are assigned in individual
cases--flood protection, water quality control, navigation,
hydroelectric power, recreation, silt detention, etcetera--they tend
often to be the most economic sources of big quantities of water. In one
form or another they have been built from very ancient times, and they
have been indispensable to the useful development of water resources in
our expansive economy.

In parts of the United States far from sea-coasts or large natural
lakes, reservoirs built for water supply and other purposes have become
the focus of enormously popular forms of recreation that would otherwise
be impossible in those regions--sailing and motorboating and
water-skiing and the sort of fishing possible only on big water, and
such things. Properly designed and located, they can be beautiful bodies
of water, as the vacation homes that grow up around many of them
testify.

Strong objections to them also frequently are voiced. They are one of
the most massive manifestations of man's technological ability to adapt
natural processes to his use, and they sometimes have profound effects
on fish and wildlife and the whole ecology of a stream system regio