Then surely it is not ice
Definition of ice: frozen water, a brittle transparent crystalline solid.
That's a fairly strict definition. Realistically, "ice" can refer to any frozen substances
resembling water ice. I mean, take comets for example. Their nucleus is typically made up of all manner of frozen gasses (methane, carbon dioxide, ammonia, etc.), and yet is still typically referred to as "ice".
Elite is fairly distopia-esq, I dont think selling water would be out the question universe wise.
The snag is you would need it super-compressed or something else the quantitys wouldn't work.
Well there's a snag with that, too: Water is strange in that you can't really compress it. Typically, when you compress a gas it turns into a liquid, and when you compress a liquid, it turns into a solid. The trick with water though is that its solid form (ice) is actually
less dense than water. That is, it takes up more space, not less. This is why pipes burst in the winter. When the water inside freezes, it takes up more space and the pipes can't handle it.
On topic: It would be interesting if you could mine from ice, but with a different type of laser, and for different types of resources (gasses, perhaps?). It would give an advantage to larger mining ships (able to bring several different types of lasers), and would make things a little more varied.