Where the water came from is a great question.
When the moon was warmer after it was formed, and maybe from bombardments of comets & asteroids. But because it’s only about 300 miles in diameter. I wouldn’t think there would be enough gravity to hold back evaporating water vapour.
So maybe it was never liquid on the surface, but the stress of Jupitor’s immense gravity and that from the other huge moons may be heating the moon under the ice causing liquid water.
I can only guess, based upon what I read, and it’s all speculation at this point.
Just have to wait for more explorations if zero doesn’t kill NASA, that is.
That would be a shame. I used to be very skeptical of NASA, but thinking ahead in the grand scheme of things, we really need to establish a significant presence off of our planet if we want to survive over the long term. Right now we are sitting ducks, with all of our eggs in one cosmic basket. Even if we could only colonize the Moon, that would certainly be better than nowhere. Right now, I think NASA is the best equipped at helping us get there, but the private sector should also be encouraged and given the freedom to help us get there as well.