At any rate, they are not an answer for Washington's problems. Even if enough of them were installed specifically to provide the storage volume needed for metropolitan use, the question of operation--ensuring and coordinating releases from a large number of places at varying long distance upstream from the point of intended use, in such a way as to make the required volumes of water arrive at the right time, without waste--would be very difficult even with much more sophisticated and expensive design than these structures customarily have. Without it the problem would be insuperable. * * * * * Thus, for metropolitan Washington's water in the near reaches of the future, some reservoir storage is indicated with fewer ecological, recreational, and scenic drawbacks than a Potomac main stem dam, and more efficiency for massive supply than the small headwater structures. Since the Potomac river system is a unit, with the metropolis at the downstream end of its non-tidal part, water stored anywhere in the upper Basin can be released for use there. This gives much freedom of choice in the selection of sites for reservoirs and in the combination of releases from various places to make up an adequate total supply, though obviously good management will be needed to coordinate the releases and avoid the waste of water. It also means, if good principles of river-basin management are followed, that reservoirs to supply water at Washington can be located and designed so as to satisfy major upstream demands at the same time, and that they can be fitted in with regional and Basin needs for water quality improvement, flat water recreation, and in some places flood protection. In such conjunctive planning, based in the Basin's physical unity, commencing now and continuing on into the future as new needs and new ways of satisfying them come to view, lies the main hope of developing the Potomac water resource in such a way as to avoid waste of money, waste of water itself, and waste of the landscape and the general environment. Without it, nothing can result but a piecemeal haggling to bits of the river system as local demands grow acute and local pressures force the adoption of one-shot measures. With it, towns and areas and industries can be guided toward sensible and thrifty action that fits in with the wellbeing of the whole Potomac region--toward buying a share in the water of a rightly designed, rightly placed reservoir large or small, toward development of ground water resources where these are adequate, toward the use of new technology that may be feasible and suitable. [Illustration] [Illustration]