Thunder, do they all (the drinking-with-meals majority) have problems with digestion of food? I don’t know about all, but indigestion is a major, major, major problem for many in the US. Walk into any drugstore and look at all the OTC products for various digestion woes. And at least for a while, prescription heartburn meds were top sellers. I’ve seen lots of people guzzle a drink with their meals, and then chase it all down with Pepto-Bismol. Their problems may not be caused by drinking with meals, but logic isn’t going to uncover the answer here.
I don’t think any science backs up the don’t-drink-water recommendation. But I usually don’t drink anything with meals, because I feel better that way. Some people seem to have poor digestion, and anything that improves it really matters. Others have great digestion and can do whatever they want. The cliche is “iron stomach.”
So my advice is to try it both ways, and record how you feel afterwards. If you are not digesting your food well, you will know.