What you need:
water bottle with cap
aluminum can or other metals you can cut
motor (one that spins fast?)
tubing (copper or other source...)
power source (3 - 9 volts)
hot glue gun
Step 1: Prepare the bottle cap
Drill a hole in the middle of the bottle cap making sure its centered about the same size of the middle of the motor so it fits in. Drill a hole in the side big enough for the tubing going out. Don't forget to drill a hole in the bottle cap so the tubing can flow out.
Step 2: Motor and impeller
Hot Glue your motor onto the bottle cap and make sure it spins by hooking it up to a power supply. (It doesn't need to be water proof...) If you haven't screwed the neck off yet do so now. (It'll make things a lot easier.) Hot glue your impeller to your motors shaft and let it cool. Screw your bottles neck back on and your done with this step..