大雪海のカイナ

1. How did Kaina calculate 30 days, and then just a bit later got 3 days? And then it looked as if it took them only 2 days.
2. Why does it look as if that was the 1st time she was peeing since the start of descent? Even assuming they did not drink or eat anything (which was not the case), this does not look plausible.
3. What's the point of glasses, if they are not wearing them?
4. What's the point of oxygen mask, of it's used only once randomly? If there was a need for it (due to height), then they should have been using those for quite awhile.

Also, I think the catch would be that there is something under that snow see

That looked like water under the snow clouds or whatever. Why can't they filter that? Or if it is not water, but some other liquid, it is still probably made of hydrogen and/or oxygen, thus they could get water from it. I mean there aren't that many transparent liquids without both. And while they do not seem high-tech, if there was a necessity, they would still figure something out.

That was a very thin line they used to get of the water. I do not believe it could be used in real life neither to climb it (too little surface) or to pull a human out without some contraption like on fishing rods (especially without piercing something).

It also dawn on me: this world lacks water, but there are no indications they lack food, even among poor people. Which while not completely impossible still feels a bit off.

So long into the story and I just now started questioning: why did people in this world dropped written language? I would expect ability to read amd write to become sparse, but vanish completely? What would cause that?