This experiment demonstrates the heat of the sun turning the water in the tub/bowl to vapor (evaporation). The vapor turning back to water droplets on the plastic wrap (condensation), drops getting too heavy and falling back down (precipitation) to the water in the glass which represents land (collection).
The evaporation and condensation are the key terms that help water purifying. While these processes occurs during the water cycle, it can also be used to purify water for drinking or industry use. Water is always moving. The movement is driven by the energy of the sun and the force of gravity.
Precipitation is water released from clouds in the form of rain, freezing rain, sleet, snow, or hail. It is the primary connection in the water cycle that provides for the delivery of atmospheric water to the Earth. Most precipitation falls as rain.