One thing that can be very fun is asking people to participate in a "blind" taste test to see if they can tell which of two waters is from the tap and which is bottled.  I've heard of a number of schools doing events like that as part of Food and Water Watch's "Take Back the Tap" campaign.  Give away your reusable bottle to anyone that particpates in the blind taste test.  Everyone will have a lot of fun trying to figure out if bottled water really tastes better.  From their website, it looks like Food and Water Watch can give you fact sheets and other materials to help with your tabling effort.

Sam Hummel
Database Administrator
AASHE

Hi Shane,

I once attended an event where they created giant Jenga-like towers of empty reusable water bottles.  Participants could come up and try to take the water bottle down without destroying the whole tower.  This does not really accomplish the thought provocation you might be hoping for, but it did gather a large, engaged audience because of how fun it was to watch and participate.  It was so fun when someone would finally topple over the tower!  The bottles all had decals on them with some tidbits of information on the impact of using tap water as opposed to bottled. 

Kyle