You will need a bowl of water with a clean sponge in it, two glasses (one ordinary, and one pretty), and a pitcher of water (preferably a pretty pitcher).

Look at one person in the room and say, "You look thirsty."  Proceed to make a glass of water by squeezing the sponge into the ordinary glass. Hand the person the glass. (They will either look at you funny or say, "No, thanks".)  Then say something like, "Oh, it's fresh water and a brand new sponge.  It's fine."  (Again, they will refuse. You set aside this glass on the table.)

Then, pour a glass of water from the pitcher into the pretty glass.  Offer this glass and ask, "Would you like this better?" (Give them this glass.)

Pause and then say, "The way you serve up the gospel matters."