I'm confused.
If we pick to only drink water until we die, we can surely still eat whatever we want.
If we pick to only eat food until we die, we can surely still drink whatever we want.
If we aren't eating food, I don't know what else we are supposed to be eating.
So if we pick option 2 and only eat food until we die, we can continue to eat and drink whatever we like and it is the clear and obvious choice.
If you mean that if we pick either one we can't do the other (and by implication anything else), it could be argued that certain foods would provide the fluid intake needed to survive meaning option 2 remains the sensible choice for longevity, but for that quality of life and in the absence of being able to do anything else I'd rather not live.