I'm not a physicist, and this question is bugging me .. :)
Is it possible to create a closed power-generation system, using upper and lower water-reservoirs where a continuous flow from the upper to the lower turns a waterwheel (or series of..) with an elongated axle(s) to which several generators are attached with bevel-gears, by using the power generated by some of the generators to pump water back to the upper reservoir at the same rate as the outflow, and the remaining generators feed the grid?
Based on the comments and answers:
(and I'm not fooling about, I really want to understand)
Say you have one waterwheel with one generator attached which gives say 50% efficiency (can return 50% of the used water to the upper reservoir, all friction, heat-loss, etc, taken into account); Now you add 2 more generators to the waterwheel's elongated axle: the output of two of these generators will return 100% of the water, and the output of the third is available for use. There can be a cascading set of waterwheels each with generators attached..
Why would this not work, what am I not seeing?
[PS:]Wasn't it Archimedes who said something about a long-enough lever and a place to stand and he will move the earth? Meaning that a small input (muscle-power in this case) can have much larger output. A waterwheel is nothing less than a lever, and so are the gears, ...