Are Quick and Slow Death Different?

In the post The Principle of Double Effect and Abortion, or more precisely, in a comment on the post, the example was given, taken from Steven Long, of two persons in a space capsule with a limited air supply. There would be enough air for one of the persons to reach earth safely, but not for both. Moreover, one person is mortally allergic to an anti-viral agent in the air, and so will die in any case. The question was raised, can the other person deny him air by ejecting him from the spaceship?

I would like to compare this case with a analogous case inspired by my last post. Two persons are on a island with just barely enough water for one person. Again, one person is allergic to something in the water, and will die in three to four weeks if he drinks it–whereas he will die in one to two weeks if he does not. Can the other person deny him water, by force if necessary, or is this murder?

Steven Long asks, apparently, rhetorically, "By moving him, do we not in fact hasten his death? If we deliberately hasten the death of another—and let us suppose we do so against his will—do we not then commit murder?" I think in terms of people's instincts, it makes a tremendous difference how much the death of another person is hastened by our action, that ejecting someone from a spaceship, where he will die immediately, is much more revolting and instinctively wrong (at least to persons who are not in that situation; I would not be surprised to find that the moral instincts of persons on both sides who were actually in such a situation were much less strongly against this action) than denying a person water that is anyway poisonous to him, and thus shortening his life span from about three weeks to one week.

Is this right? Are your instinctive judgments regarding the two cases the same or different? Is denying someone water that would kill him anyway over a space of three weeks seem instinctively the same or different than denying him air that would kill him over a space of one week?