As you drink an ice-cold beverage on a warm day, the outside of the glass or bottle becomes wet. Why?
Water forms on the outside of a cool glass on a hot day due to condensation. The air around us has water in it; the water is in a gaseous form, commonly called water vapor. Typically, the hotter the day is the more water is evaporated into the air.
When you have a glass with ice in it on a hot day the glass is cold due to the contact with the ice. The glass is also in contact with the air around it, which has water vapor in it. When the water vapor comes into contact with the glass it cools down and turns into the liquid state of water. It resides directly on the glass because that’s the only place it cools down enough to actually become water.
It is same principle that makes the mirror in your bathroom fog up after a hot shower. The water in the air is cooling when it touches the mirror, as well as the walls but you don’t noticed that because the wall still looks pretty much the same.