This is where my knowledge fails, but I think it's safe to say that different chemical and filtration processes activate between different classes of in-taken nutrients including water, and these are handled by different organs in the body.

The intestines do much of the work of digestion for more complex molecules, giving those molecules time to be broken down into protein building blocks, and simplifying starches into sugars. But if you drink a couple big glasses of water, most of that water never reaches the full path through them.