Water Can Exist in Three States Simultaneously at a Specific Temperature and Pressure

Water's triple point is one of science's most elegant phenomena. At exactly 273.16 K (0.01°C, 32.018°F) and 611.73 pascals of pressure, water simultaneously exists as solid ice, liquid water, and water vapor — all three states at once. This unique condition is called the 'triple point.'

The triple point is so precisely defined that it was used as a reference point for the international temperature scale for decades. Below this pressure, water cannot exist as a liquid — it goes directly from solid to gas in a process called sublimation (which is how freeze-drying works). The triple point demonstrates that the state of matter depends on both temperature AND pressure simultaneously.