@BowsacNoodle @Rayfield My dictionary of the middle ages actually has a section on waterwheels. Most of all the water wheels to ever exist were horizontal, but no designs survived until today (that is, written designs, many artifacts remain). On the other hand there are many historical schematics for vertical water wheels. Which used gears to mill at much higher speeds.

If I had to guess, if you measured the flow rate, and max elevation difference, you can derive the wheel radius. Then it is a matter of splitting the torch between speed (V) and reserved torch for Amps. (the split is probably dictated by what the engine is tuned to receive? Enough Volts so you don't burn the wires?)