what is the triple point of water

The triple point of water is the unique temperature and pressure at which ice, liquid water, and water vapor all coexist in stable equilibrium.

Quick Scoop

• At the triple point, water is simultaneously solid, liquid, and gas.

• For water, this happens at:
  • Temperature: 0.01 °C (273.16 K).

* Pressure: about 611.66 pascals, or roughly 0.006 atm.

• It is a single, very specific combination of temperature and pressure, not a range.

Why it matters

• It is used as a fundamental reference point to calibrate very precise thermometers, because 273.16 K at the triple point of water historically defined the kelvin.

• On a phase diagram (pressure vs temperature), the triple point is where the lines separating solid–liquid, liquid–gas, and solid–gas all meet.

A simple way to picture it

Imagine a tiny sealed chamber with ultra-precise control of temperature and pressure.
If you tune it exactly to 0.01 °C and about 611 pascals, you can watch ice, liquid water, and steam all present at once, with ice melting, water boiling, and vapor condensing in continuous balance.

Information gathered from public forums or data available on the internet and portrayed here.