Temperature is the determining factor for water's state of matter. Temperature is a measure of the average kinetic energy contained by each molecule in a given volume of space. It describes how quickly particles are moving or vibrating. Water, like all molecular substances, has a set boiling point and freezing point. Those set temperature points do not change. It is true that on other planets, water has different set points for boiling and freezing. Factors such as atmospheric pressure and gravity affect the temperatures at which matter changes states. On the planet earth however, temperature is the only measure that always corresponds to the state of matter a particular substance takes.