Fill a jar with hot tap water and then pour out half.
Cover the jar with plastic wrap.
Place several ice cubes on the top of the plastic.
The hot water evaporates, collects into clouds, and then it will rain down little droplets after some time off of the plastic wrap up top when it becomes to heavy. You can help it along a bit by poking it. ;)
We also used this site: http://www.epa.gov/safewater/kids/flash/flash_watercycle.html