What you need:
1.A medium sized bowl
Put the water in the medium size bowl and fill it quarter of the way.
Put the mug right sized up in your bowl.
Put the glad wrap over the bowl then seal it with some string or some rubber bands.
Put the bowl in the sun and wait and observe.
I predict that it will evaporate and leave little water droplets on the top of the bowl.
My prediction was kind of correct.
The sun heated up the water and it evaporated up towards the glad wrap. Condensation formed on the glad wrap. When water vapor became heavy it dropped in to the cup like rain. (precipitation)