The simplest way to deal with this is to have your dad get a note from his doctor that says that he can only drink bottled water. He may still get grief (see below), but at least he'll have something to help make his argument.

The reason I say that he may still get grief is that restaurants can be nervous about outside items coming in. Mostly, of course, but they fear it cuts into their profits. But also because it raises concerns about what's being brought in (is it really water or is vodka?) and safety issues (will TOG be blamed if the water he brings in is contaminated). You point about the baby is valid.

I say that if the bottle is sealed and he has a doctor's note, then TOG needs to butt out.

If not, then unfortunately he'll need to stop eating there. I have a particular place that I no longer eat because I get sick from something in their food.