bottle of water

[mferster]

hmmmm, you could try adding some subtle width variation of the inside glass faces and increasing the thickness near the bottom and the top a bit more. See if that makes it look closer.

[cjwidd]

Yeah, deforming the inner faces with some noise might be a good idea. I did, however, apply a noise to the bump channel of the water body, which helps to create a similar effect.

Something I haven't tried is creating a car paint-like shader to create a layered effect, but I know that would increase the render times even more.