I made a water wheel for my parents' pond. 

It's really easy to assemble and all the parts are printable.

1. Take the "body" and glue "arm1" and "arm2" to it.
2. Prepare "wheel1" or "wheel2" (the choice is yours), insert "rod1" into the wheel, drop glue into the hexagon hole of "rod2" and insert it into the wheel to "rod1".
3. Finally, just insert the complete wheel between "arm1" and "arm2" and you're done!

The body is prepared for a 40mm tube.

I recommend PETG material.

You can see how to print individual parts in the photos!