I just put myself in the minds of these alien beings and try to come up with this. They were as meaningless as possible so that they d convey otherworldliness. I guess that s an instinctive choice and maybe that has something to do with the dreams I had as a kid. There s an element to this film that s hard to explain. There is no reason for that, other than it appealed to me.
Simple answer is that they re human things.
Light and water are the two things we need to live. We re primarily made up of water. That s really the simple answer. To me, the answer within the logic of the movie is that if you put human things into a situation like the one in DARK CITY you suppress them and you experiment on them for a long enough time that humanity will find some way of dealing with that situation. I think human beings are incredibly adaptable creatures and they will somehow reconfigure themselves to deal with the situation, and what I m saying in the film is that exactly.