While preschoolers see the effects of precipitation during rain or snow, they may not be as familiar with other parts of the water cycle, such as evaporation and condensation. Evaporation happens when water turns from a liquid back into a gas while condensation marks the change of water from a vapour back to a liquid as it cools.
Once you have explained that water usually first makes its appearance on earth as precipitation in the form of rain or snow, demonstrate how the water disappears into the air again to explain one of the basic steps in the water cycle. Fill two cups equally full of water and mark the level with black marker. Seal one cup with cling film and leave the other open. Place both cups near a window and check the cups on a daily basis, marking any changes in the water level. Preschoolers will be amazed as the water in the open cup disappears into thin air.
Ice cold condensation
Water turns from a gas to a liquid when warm air filled with water vapour hits something cold, so demonstrate condensation with a simple science activity using only a glass of ice water. Fill a glass with ice water and let it sit for a few minutes. Watch as tiny droplets of water bead on the outside of the glass as the warm water vapour-filled air meets the cold glass to form condensation. Explain to students that clouds are actually formed by condensation as water in its gaseous form rises from the earth and cools.
Demonstrate evaporation and condensation hand-in-hand with a kettle and a piece of cardboard or book. Place an 21.3 x 27.5 cm (8 1/2 x 11 inch) sheet of cardboard in the freezer while you boil a kettle of water on the stove. Invite preschoolers to observe the steam rising out of the kettle created by the water getting hotter and turning from a liquid to a gas, evaporating into the air as they watch. Wear oven gloves to hold the frozen cardboard 30 cm (1 foot) above the spout in the steam to see how the hot, evaporating water turns back to a liquid through condensation when it hits the cold surface.
Cotton ball clouds
Preschoolers will grasp the concepts of evaporation and condensation when they can hold a cloud in the palm of their hand. Pass a cotton ball cloud to each child and spread a few shallow pans filled with 1.3 cm (1/2 inch) of cold water among small groups of preschoolers. Ask them to describe how their cloud feels when it is dry, as if the cloud had just rained or snowed. Have them warm up the water-filled pan lake by blowing warm air onto the water to make it "evaporate" back into the air. Dip the cotton balls into the water as you explain that the air is cooler way up high in the sky, so the water turns back into a liquid during condensation to form a cloud. If you are explaining the entire water cycle, you can now invite students to squeeze the water back out of their cloud into the lake to simulate precipitation.