water to drink

Can someone please explain why in some contexts "water to drink" is prefered over "drinking water", when 'to drink' serves as an adjectival phrase? To me, they both are adjectives, so I would choose the one I'm most familiar with which is 'drinking water'. Why make your life harder? Is this a matter of preference?

For example:

So what's the best water to drink? or What's the best drinking water?



I'm certain that there are contexts where 'drinking water' cannot substitute 'water to drink'. Otherwise, there wouldn't be the phase "water to drink" in the first place. One type of example I found on Google is :

How much water to drink? => However, I believe 'to drink' here is adverbial, not adjectival. How do I know? It's because it can't be replaced by the adjective drinking and still retain the same meaning

* How much drinking water? => the meaning has changed from " how much water a person should consume" to "how much water there is".

Maybe I'm wrong and 'to drink' is adjectival. In that case, I don't understand why 'to drink' is adjectival as it sounds like an action.

Can someone please clarify this?Thanks!