Water drops that collect on a
cold glass of lemonade come
from

The condensation of water vapor present within the air around the glass

Explanation:

Hello there! When a cold glass is left unattended the outer rim of the glass is exposed to air. Condensation of water vapor that is ever present within the atmosphere will form water on the outside of the glass in reaction to the cold surface.

On another note, water can also be seen forming on the outside of surfaces of cold bottles due in part to osmosis. osmosis is the process by which molecules will pass through a semi permeable membrane layer in order to equalize the pressure on both sides of the membrane.

Hope this helps!

-HM