As described and displayed in this discussion, you can see that in a room full of water the tiles at the bottom of the room are denser than the tiles at the top. Presumably this is supposed to reflect the increased fluid pressure in the bottom tiles, but only gases behave this way to any significant degree, not solids or liquids. Here's the Wikipedia article on water that describes the compressibility of water. Basically, at 400 atmospheres of pressure water only compresses less than 2%.
Octyabr's discussion linked in the description shows steps to reproduce the issue. But basically just fill up a room with water and notice that the bottom tiles have a significantly higher density than the upper ones.