system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Where did all of Earth's water come from?
gpt
Scientists don't really *know* for sure where all of our water came from, but it's exceedingly likely that our water came to us in the form of icy objects like comets.  Some of it probably came from the rocky material of the Earth itself as the planet cooled and condensed.  There probably wasn't just one source.