I think OP knows exactly what they mean, I think if you asked a five year old they’d know what they mean.

Yet for some reason, some people are completely missing the point of a very simple question which boils down to “if you couldn’t drink regular water, what would you have instead”…

The point of OP's question is clear. He's referring to a drink that has sensory qualities that are clearly distinct from plain water. Water with a spritz of lemon still reads as water. As a loose guideline this is like anything you'd order as "water with x" or "x water", like cucumber water. Coffee clearly doesn't fit into that category, it has sensory qualities that are very different than water with x in it.