According to many Southern Baptists, it was water-to-grape-juice...
Grape-juice at a wedding? At a Jewish wedding?
Also, from John 2:10 "Every man serves the good wine first; and when men have drunk freely, then the poor wine; but you have kept the good wine until now." Anyone reading this passage can see that grape juice is not the topic of conversation. You get the guys buzzed with the good stuff, and then give them the cheapo stuff.
I never could figure out why my pastor was so hung up on grape juice. I believe it is sinful to drink in excess and be drunk, but a moderate use of alcohol I feel is allowable.