s from the river above the Fall
Line, local storm runoff and tributary flows, and treated sewage
returned to the tidal river. The volume of this water that would be
available for use without salinity has been variously estimated. At low
tide, there would be 9 billion gallons of fresh water in the upper
estuary from Chain Bridge to the mouth of the Anacostia River; In the 10
mile stretch from Chain Bridge to the District of Columbia's Blue Plains
treatment plant, 15 billion gallons; and, from Chain Bridge to the
saltwater front near Indian Head, Maryland, 100 billion gallons. Most of
the time now it is afflicted with heavy pollution, as will be detailed
in the next chapter of this report. But it does constitute a large
natural reservoir of potentially usable municipal and industrial water,
whose attractiveness for these purposes, as well as for all others, will
grow steadily as the pollution is brought under better and better
control. These facts have led some opponents of any and all major
reservoirs in the Basin to conclude that the water in the upper estuary
is a presently satisfactory reserve with which to face any foreseeable
metropolitan shortage of supply from the upper Potomac.

The assumption has strong appeal, but it appears to be too risky to
serve as a basis for adequate present planning to meet looming demands.
That even now the water in the estuary's uppermost reaches, above the
main metropolitan treatment-plant outfalls, would be usable for short
emergencies by the installation of relatively simple pumping equipment
below the falls, cannot be doubted. That in the long run the major part
of the freshwater tidal river at and below Washington is likely to be a
valuable source of metropolitan water, maybe a principal source, is
quite possible. Its use is and will be a strong consideration in
longterm planning--another good reason, in fact, for flexibility. But
the truth is that right now enough doubt and ignorance exist in regard
to its exact potentiality that it should not be counted on to provide a
safe margin of supply under all conceivable conditions during the next
twenty years or so, for which planning provisions need to be more rigid
and definite.

The doubts and unknown factors have to do mainly with the quality of
this water, which comes under discussion later. In abridged summary of
relevant facts at this point, it may be observed that unless all sewage
and sewage effluents were collected and divert