Hi, I just came across your question and want to say I have the very same problem, except I don't drink as much water. I went to a general doctor and she put me on pills, but for acid reflix thinking that contributes to it, my pills have worked with acid reflex, however, I still have bloating.
But once I went to a natural doctor that a friend took me to, and believe it or not, he gave me fiber to take everyday and told me to stay away from cheese and bread and actually that worked. My stomach was not bloating anymore. I didn't think I needed that fiber because I thought I was fine in that area, but apparently that was the problem. I haven't been back to him to get some more, it's been about three years and i'm bloated everday again. If I just drink water or coke my stomach will bloat. Oh, also one more thing. He felt my stomach as I was lying down and said my intestines didn't feel right. So that could be my problem to, and maybe yours. I think I should go to an intestinal doc to get xrays but I still haven't. Maybe you should to. Hope this helps a bit.