its the basic water wheel system based on the Haris design of wheel used in hydro electric dams.
Step 1: Starts with a bicycle wheel
you need to weld the spindel to the main wheel so when it spins it spins the wheel with it not just the spindel on its own, you could take this out and replace it with a long rod which will go off to our generator.
Step 2: Attach the generator
the generator is a simple car alternator, i would recommend putting this inside a rabbit hutch or something simlar, just drill a hole in side and poke the rod through this will keep the rain and splash back from the wheel off the generator.
Step 3: Adding the cups
by using hot glue it means it wont react with the water and go mushy like some glues would.
Step 4: Placement
place a flume above the wheel so that the end comes past the center of the wheel, guttering is ideal for this.
you will need a water source as well, ideally you would have a stream running through your garden so you could use that to channel water down your flume and run your wheel.
so it works by water coming down the flume, hitting the wheel, the weight and force of the water turn the wheel generating electricity through our alternator which can be hooked up to charge car batterys or leisure batterys for cars, electric fences (if your on a farm), or for other projects, you could even hook you phone up to it to charge it by water power.
i would like to make another suggestion, if you channel the drain pipe from you house to the flume the rain water collected from your house can be used in the wheel and then you could channel it to a water butt or drain. this would work really well here in the UK where we have a fair bit of rain.