Puddles

[Buster Brown]

Why does water appear on the side of a glass full of cold water, leaving a puddle on the coaster when the glass is lifted?

[boobesque]

the condensation is formed due to the glass being warmer than the water. The condensation forms into water droplets that run down the side of the glass.

[Skids]

The glass is cooled by the liquid it contains to the liquid's temperature.  In an environment such as a warm humid day, the water droplets in the air condense as they come into contact with the colder glass.  It collects then dribbles down the glass.

[alphamale]

....or, you spilled it.

[brachiopod]

I must admit that I am conversant with this phenomenon occurring with my glass / can / bottle of cider, but what is a glass of water?