Because it's a very real thing. And they have T-shirts!
But here's the crux of the matter: I have been all over that website and nowhere on it -- nowhere! -- does it say, "Exclusive water supplier to the national conventions of all major political parties." Why do you suppose they'd want to hide an important distinction like that?
(And yes, that paragraph's satire. Crazy Water most certainly is not, having been a fine product out of Mineral Wells, Texas since the Nineteenth Century. As you might except, that's where the name of the town comes from, and I am assured by those who can obtain it that it's very fine mineral water indeed.)
8 months ago