UFO's

[Anomalocaris]

'Wot ho, Cyril - what about invading India, then?'  'Nah, Clive.  They're at a lower technological level than us, they've got nothing we'd want.'

Boru

If these boys were to discover how much water we have;
Then-We-Are-Fucked.



Or mebbie not. Arrakis orbits the star Canopus which is ~300 light years from Earth, they would need a mighty telescope to spot a water world at that distance.

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.
An interstellar drive system must use some sort of ion/photon/plasma drive and that wouldn't need much water.
Other than water what does planet Earth have that they can't find in the millions of planets much closer to their home world?

But then again, I could be talking shite.

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.