4 tons of water is smaller than a cube 6ft on the side. Water flows where you want it, it’s disposable without special procedures, and is literally available an

4 tons of water is smaller than a cube 6ft on the side. Water flows where you want it, it’s disposable without special procedures, and is literally available anywhere out of the tap. This doesn’t seem like the hard part. Edit: sibling comment points out that helium can also be compressed. I don’t think “too much lift” is an intractable issue.