I've heard of a water diet, but it was a different version. It wasn't a glassful for every mouthful, but a full glass of water at least 15 minutes before each meal and one in between meals.

I think a glass of water with every mouthful could be dangerous, as too much water is actually harmful. It's called hyperhydration or something like that. If you live in a very hot climate and sweat a lot it may not be such a problem.