Water is very important for our world. It moves in a large circle. This big movement is called the water cycle. The sun gives the energy for this cycle. First, the sun heats water in oceans and lakes. The water changes into a gas called water vapor. This part of the cycle is evaporation. The water vapor goes up into the sky. The air high in the sky is cold. The water vapor cools and becomes tiny water drops. These drops form clouds. This change is condensation. When the clouds are full, the water falls back to the ground. This is called precipitation. Rain is a form of precipitation. The water collects again in rivers and oceans, and the cycle starts again.