GW/
I haven’t proceeded any further for years, but recently (November, 2020) had an insight…
MOST of the torque generated by such a wheel occurs in the middle third.
So the water ‘back pressure’ could be significantly reduced if the wheel ‘enters’ the reservoir at about 1/3 up from the bottom of the wheel, NOT at the bottom of the wheel.
This would significantly reduce the back pressure without significantly reducing the wheel’s potential torque.