system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why when looking for life on other planets is water a prerequisite? Isn't it possible that some alien life forms can exist without water? Or is "life" just a very specific term?

I've just always wondered why it's assumed that all life forms necessarily need water, or maybe I've just got the wrong end of the stick. Either way, feel free to enlighten me.
gpt
Water can dissolve a huge range of things in it, and living things will (probably) require a lot of complex chemical reactions that will need to happen in a solution.  For instance, our own cells are more or less little bags of water with lots of chemical reactions happening inside that wouldn't happen if they weren't in a liquid.

Is water absolutely necessary?  We can't know.  But it seeks like the best bet to look for, since it has peculiar properties that allow for a lot of interesting chemistry, and also because it's a very simple molecule, made of two very common elements, so it's all over the place.  It's very possible though that there is life out there at very low temperatures that uses liquid methane or something.