The water cycle is the continuous movement of water on Earth. The sun heats water in oceans, lakes, and rivers, turning some of it into water vapor (a gas) that rises into the air -- this is evaporation. High in the sky, the water vapor cools and turns back into tiny water droplets that form clouds -- this is condensation. When enough droplets collect, they fall as rain or snow -- this is precipitation. The water flows into rivers, soaks into the ground, and returns to oceans and lakes, where the cycle starts again.
Draw the water cycle as a diagram with labeled arrows. Boil water and show steam rising (evaporation), then hold a cold plate above the steam to show droplets forming (condensation). Place a cup of water in the sun and mark the water level each day to observe evaporation. Use the terms evaporation, condensation, and precipitation consistently.
Have you ever wondered where rain comes from? Or where a puddle goes when it dries up? The answer to both questions is the same: the water cycle. Water is constantly moving around Earth, changing between liquid, gas, and solid, traveling from the ground to the sky and back again.
It starts with the sun. When sunlight shines on water in the ocean, a lake, or even a puddle, it heats the water. Some of that water gains enough energy to turn into an invisible gas called water vapor. This process is called evaporation. You have seen it happen: a puddle on a sunny sidewalk slowly shrinks and eventually disappears. The water did not vanish -- it evaporated into the air.
The water vapor rises up into the atmosphere. Higher up, the air is cooler. When the water vapor cools enough, it turns back into tiny liquid water droplets. This is called condensation, and it is how clouds form. Each cloud is made of billions of these tiny droplets clinging to microscopic particles of dust or salt floating in the air. The cloud is essentially water that evaporated from the surface and condensed high in the sky.
When enough water droplets collect in a cloud and grow large and heavy, they fall back to Earth. This is called precipitation -- rain, snow, sleet, or hail, depending on the temperature. The rain flows into streams, rivers, lakes, and oceans. Some soaks into the ground and becomes groundwater. From there, the sun heats it again, evaporation begins again, and the cycle continues. The water on Earth today is the same water that has been cycling for billions of years. Nothing is added, nothing is lost -- it just keeps moving.