I just re read PBAs original post.
If someone is already in middle of the way/hike and wants to eat bread and knows for a fact that the is no water within the next three mil (72 min).
In my personal opinion, he should not use the water for shing the hands, since he will have no water left for survival. (since he knows that the is no other water in the area, hiking without water is definatley dangerous).
However, he has the option to wash and save the water for drinking.
It’s not a real tumah.