I have designed, and live with a hydro system every day.
Do you really believe that I have no idea of how it works or what it takes to make it work?
The reservoir only needs to be big enough to hold one cycle of generation between recirculation events.
That, may be less than you think depending on the system that is adopted.
That is one advantage of pumped hydro, you don't need to keep finding external water to make it work.
That is one reason I cant understand why people seem to think that pumped hydro wont work in a dry area, even a desert. You only need to replace the losses due to evaporation etc. It doesn't matter where it is situated in the landscape.
If you had pumps recirculating the full amount of water continuously then you would only need the amount of water that it takes to fill the system plus expansion and contraction and a supply tank big enough to stop the system sucking air.
