UFO's

[Anomalocaris]

Uh, >>90% of the water in our solar system is not on earth.   If our understanding of the process of planetary formation is correct, then most planetary systems would contain many times more water than present on earth, many of these would have them concentrated on large outer planets and moons.

Apologies for being unclear, what I was stating in a rather vague roundabout way is, why does a starship need water?

Water may indeed be a valuable resource for an interstellar spaceship, growing petunias or whatever but as a reaction mass for a propulsion system then that is one piss poor starship drive they have.

Edit:

Other than water what does planet Earth have that they can't find in the millions of planets much closer to their home world?

Yes I see your point. My bad.

Water as reaction mass for a propulsion system may not seem nearly science fictiony enough for an future age we are told that would be populated by warp factors and Alcubierri drives,  but there seems to be no reason why such reaction propulsion systems can not form the basis of interstellar civilization.

Right conceited yokels we would seem if several hundred years in the future, we are still stuck on this planet pining away for faster than light technology, and scrappy adventurous aliens in chemical rockets a century or two behind our own technology curve come down and demand to see our leaders.