According to the phase diagram for water, how is the state of water determined?

Explanation: Phase diagram of water is attached below.

In a phase diagram, the point lying between the two curves represent the physical state. Any point on the curve represent that two states are in equilibrium. The intersection of the three curves represent a triple point which means that all the three states are in equilibrium.

For example,

Point Y = This represents the water is in gaseous state.

Point X = This represents the equilibrium between solid state and liquid state.

Point O = This represents the equilibrium between all the three states of water.