Does non-buoyant water even exist? If so, how is it different from regular water?
Non-buoyant water isn’t really a thing. All water is buoyant, but mixing it with air or gas reduces its density and makes it seem less supportive.
Exactly. For water to lose buoyancy completely, gravity would have to disappear, like in space. It’s an interesting thought, but not something we deal with on Earth.
The term ‘non-buoyant water’ is misleading. What people usually mean is aerated water, which can reduce floating capacity temporarily.