Alex Breitler has done us all a useful service, not only debunking the Not Twain “Whiskey’s for drinkin'” quote but also pinning down, via Barbara Schmidt, where it first got attached to Twain:
She believes, based on a Google Books search, that the quote probably was first attributed to Twain in the 1960s.
Pingback: Whiskey, water, and Mark Twain « Water Librarian's Blog