system
Given the following post, respond as if you're commenting on Reddit:
human
Can a planet be 100% water?

Can a planet be completely made of water, or any other liquid? Or is some land and layers inevitable?
gpt
Liquid at what temperature and pressure? You could construct a planet made entirely of H2O, but it would have an ice core and at least some gaseous atmosphere.  If it were another substance, the same would be true.

If it were a non-metal liquid, it would quickly evaporate into space from sputtering due to the lack of a magnetosphere. 

This planet could not survive, and probably wouldn't even ever form naturally.