That's not something I have ever heard of before! This probably isn't related to your particular question, but on a recent episode of 'House MD', there was a guy that was drinking a whole lot of water, and one of the doctors said that could cause him to have low sodium (lower than what is considered normal). I don't know if there's any correllation between having low sodium and being really thirsty....doesn't seem like their would be....but I felt inclined to mention it all the same!

But it does bring to mind that perhaps since you are drinking alot of water, maybe you aren't getting enough of a certain vitamin/mineral...maybe its getting flushed out of your system by the water and you aren't replacing it with food or a vitamin supplement? That could be the reason for your thirst I guess! Hopefully someone else will have a better answer for you, but in the meantime....if I were you, I would probably start taking a multivitamin and see if that helps. It couldn't hurt!

Good luck to you!