It just causes a mess when the pig sits in it, poops in it, and pees in it.. and like mn said, that creates a hell of a lot of bacteria. So when the water is messy like that, the pig would have to drink it, causing illness, or it wouldn't drink at all, and get dehydrated..unless you could change the water dish 2 or 3 times i day, i personaly woulodn't do it..but if it works for you, and your pig doesn't mess it up at all, then go for it.