Place the glass of water on a window ledge and check it each day, observing the water level compared with the position of the rubber band. Another way to demonstrate evaporation is to put water on two separate sheets of construction paper. Let one sit undisturbed and fan the second one with a piece of cardboard. Notice the results. The water molecules are still there when the water evaporates, but they are now gas molecules in the air, and not in the glass.
Evaporation takes place faster when air is in motion.