When you say "jet pump" What is this?
A "jet pump" is a system for pumping water from a moderately deep well - say something over 30 feet deep - without having any submerged moving parts. (After about 30 feet you can put a perfect vacuum on your "straw" and not suck up any water - the atmospheric pressure isn't enough to support a water column that high.)
A jet pump system has a pump and pressure tank on the surface and the pump works across the pressure difference of the tank versus that at the top of the well. But maybe 3/4 to 4/5 of the water isn't delivered to the tank, but goes back down the well. Below the water level it turns around and then goes out a jet at the throat of a venturi. This sucks in some well water to combine with the jet and go back up the other part of the pipe.
A venturi is another sort of "water transformer", but the opposite of a ram. It trades off some pressure difference for increased flow.
The deeper the well, the higher the fraction of the water has to be recirculated into a jet to lift the water you're actually pumping. And the less efficient the system. Get deep enough and it makes more sense to sink a waterproof motor/impeller combo.
The point, though, is that an old jet-pump pumphouse unit would have a motor/turbine combo designed for a pressure difference equivalent to something like 100 feet of head and a flow of several times that you'd deliver from the well, combined with a pressure tank good for something like that pressure range.
If you've got that kind of high-head low-flow supply you just swap an alternator for the motor and get something that might not be as efficient as a purpose-built water turbine but shouldn't be too much worse. But if you've got a lower-head higher-flow situation you might make a ram out of some pipes, a couple check valves, and the pressure tank, converting it to the high-head low-flow case.
It will be interesting to hear how well this works (if at all). B-)
