We see water droplets on the outer surface of a glass containing ice‑cold water because of condensation of water vapour from the surrounding air.

What actually happens

  • The ice‑cold water inside the glass cools the glass wall, making the outer surface much colder than the surrounding air.
  • The air around the glass contains water vapour (moisture). When this warm, moist air touches the cold glass surface, it loses heat and cools down.
  • Cooler air can hold less water vapour , so some of the vapour changes from gas to liquid , forming tiny water droplets on the outside of the glass.

Why it’s not “leaking” water

  • The droplets are not from inside the glass ; they form from the moisture already present in the air.
  • This is the same physics that causes dew on grass in the morning or fog on a cold window.

Quick‑scoop table

Aspect| Explanation
---|---
Cause| Condensation of water vapour from air on a cold surface. 57
Where the water comes from| Moisture in the surrounding air, not from inside the glass. 58
Conditions that increase it| High humidity and large temperature difference between cold glass and warm air. 39

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