Books have time to get it right, movies don't.
Morally it was inhuman not to open a dialogue.
Meanwhile some of us went through this "water" thing when that last V remake was making it's rounds. But even though it's not the amount of water it's about the gravity, how much force/power is required to lift these resources into space.
Europa's surface is mostly water ice, and there is evidence that it may be covering an ocean of water or slushy ice beneath. Europa is thought to have twice as much water as does Earth. This moon intrigues astrobiologists because of its potential for having a "habitable zone." Life forms have been found thriving near subterranean volcanoes on Earth and in other extreme locations that may be analogues to what may exist on Europa.
Why send a 78 billion dollar weapon, when you could have sent 78 billion dollars of bottled water?