Hi Michael,
From what I understand, you are trying to demonstrate the conservation of energy by showing that gravitational energy (in the form of water) can be converted into electrical energy (via the turbine).
Check out these videos on a bit more of the theory and applications (they are quite good):
checkout 6:50 - similar project to yours
Probably the easiest way to demonstrate this would be to connect your apparatus to a tap. This way you vary the opening of the valve which can be your height of water or gravitational energy instead of physically moving a container higher or lower.
There are a few ways to go measure this, a flow meter like in Bryce’s post or a generator connected to a load and a voltmeter like in the second video are two good methods. By varying the flow of the tap (your theoretical potential energy) you will be able to demonstrate a change in energy at the generator or flow meter.
Hope this helps!
