Water is actually the hardest thing to swallow. Ice water or hot water will stimulate a better swallow. The carbonation and taste of soft drinks will do the same but are not nearly as helpful for hydration. The chemicals in them, coffee, tea, etc. require water in order to be flushed out by the kidneys so you don't get a s much hydration from drinking them. Much if not most of the water in them goes to flushing the kidneys, not hydrating body tissues. Juices, milk, or anything thicker than water will go down better and Thicket can be used to thicken any liquid. That is fine if he can drink enough to have a net gain in water, but " free water", water not contained in other liquids including tube feedings, is important. All things considered, a feeding tube is the easiest way to get enough water down without the risk of aspiration.