Water Can Exist in Three States Simultaneously Here

Water is unique in that it can exist in three states—solid, liquid, and gas—simultaneously under precise conditions of temperature and pressure. This unique point, known as the “triple point,” occurs at 0.01 degrees Celsius (32.018 degrees Fahrenheit) and a pressure of 611.657 pascals. At the triple point, water can coexist as ice, liquid water, and water vapor, all in equilibrium. This specific condition is used as the basis for defining the Kelvin temperature scale and the definition of the kelvin (the SI unit of temperature). It’s a fundamental concept in thermodynamics and an example of the precise conditions under which matter can exhibit unusual behaviors.