The prohibition to drink water while eating is a common stereotype, which, according to the results of recent studies, has nothing to do with reality.
If you drink water, then it does not remain in the proximal part of the stomach, but immediately enters its lower part, the distal one, from where it goes into the duodenum. Food at this time remains in the proximal section. There are studies that have measured the level of stomach acid in people who drank water on an empty stomach, or with food. The results indicate that the pH of the stomach does not change significantly as a result of drinking water.
So drink when you want within reasonable limits (not a liter or two at once), and with meals too, for acidity and digestion it will not significantly affect.
If you are thirsty, you must drink. Thirst is the best indicator that you need water. And dehydration is much more harmful to health than the mythical dilution of gastric juice.
It depends on how you drink.
If you take a bite and immediately drink without chewing, then it is really harmful. Because you replace wetting the product with saliva with wetting it with liquid and chew less thoroughly. But chewing and soaking with saliva is the primary digestion and disinfection of the product, facilitating the work of the stomach. If this is not the case, then such drinking is fraught with problems with digestion and metabolic disorders due to poor absorption.
And if you first chewed and swallowed, and then washed it down, then everything is more or less ok, but it is better not to get carried away either, as the gastric juice is diluted and the digestion process slows down. It is fraught with gas and heartburn.
This is the position of medical dietetics.
As for dry food, just food should not be only dry (especially if it is also cold), since it is more difficult to digest. And the body needs fluid.
So, if you eat sandwiches, then after eating each or half you can drink a little, but do not drink every sip :) And in such cases it is better to drink something warm, this is more useful, since the body is all he evenly heats food to the reaction temperature he needs, and here you help him, the process goes faster and less energy is needed