Substance	Critical Temperature (C)	Critical Pressure (atm.)	Density (g/cc.)
Carbon Dioxide	31.1	73.0	0.460
Water	374	217.72	0.40

Water in the critical, or supercritical, region has a density of about four-tenths that of water at 298K and behaves more or less as a dense gas. Many organic molecules, as well as O2, CO2, and N2, are miscible in all proportions with water under these conditions. In the critical and supercritical region the dielectric constant of water is from 5 to 10 while water at room temperature has a dielectric constant about 78.5.

Phase Diagram for Water