Lol, it's going to take me a while to craft a "will to live". You've brought up very good points. Terminal cancer can't be fixed, but a bullet wound can be, referring to a 4" hole. Nutrition and hydration can be hooked up via IV. When a person is dying, and I mean on death's door, water should never be denied, but I see your point about nutrition.
I'm not sure, but I think there are certain terminal renal conditions where administering water to the patient would be harmful (because there's already too much water in the body and the kidneys can't get rid of it). In conditions such as that, I would see nothing wrong with 'denying' water.