Introduction
In this phase diagram for water (CHEMIX School screen shot) we can see that water can exists as a vapor, liquid, or solid at a given temperature and pressure. The point where the three lines intersect, solid, liquid, and vapor all exist in equlibrium. This point is known as the triple point (0.001°C, 0.006 atm ). At the critical point (374°C, 225 atm - located upper right in the phase diagram for water), the temperature and pressure at which the liquid and gaseous phases of a pure stable substance become identical.
Fig. Phase diagram for water