For what its worth, efficiency wise, the best is the turbine, then overshot, then undershot. To figure head pressure, you get an extra 2.31 lbs per foot height (at sea level). There is another gadget that makes sense if you have any amount of fall, which is a ram pump. Works on water flow and can pump a lot higher than the fall itself. Of course the higher it pumps, the less goes out, but could fill a pond, or tank, on higher ground from which to power your equipment. Has a couple vacume bulbs with a foot valve, and needs no other source of power than water flow.