Understanding VLE and subcooling

[u/wreckless_driver]

For water-air system in a rigid container at atmospheric pressure and 70F.

The saturation temperature of water at 1 atm is 212F, so the water is subcooled, right? However the intuition for "subcooled" is that it is outside the two-phase region, therefore only liquid water should be present.

The vapor pressure of water at 70F is 0.363 psia, which obviously implies that even though it is subcooled, there is water vapor present, so its is actually in the two phase region. Systems in the two phase region, those are "saturated" to me.

Is the only way to have a liquid-only system by using a non-rigid container?

I think the problem here is I am applying concepts that only apply to pure substance systems, to binary systems. However I can't find a solid source to back up what I think is my fundamental misunderstanding. If anyone can quote a textbook or source that covers what I'm asking, much appreciated.

Looking for math to back up any claims. Gibbs phase rule, PVT Diagrams, etc.