The movement of water occurs in a group of repeating events. The group of repeating events is called the water cycle or hydrologic cycle. It is diagramed in the figure below. Heat from the sun causes water in oceans, lakes, swamps, rivers, plants, and even our own bodies to evaporate into water vapor. Water vapor in the atmosphere forms clouds as it cools and condenses .
Clouds are collections of millions of tiny droplets of water.
When these tiny droplets of water cool, they form larger drops of water. When the drops of water become too heavy to stay in the cloud, they fall to the Earth as precipitation . Rain, snow, sleet, and hail are all forms of precipitation. The form of precipitation that falls depends on the temperature of the air. Water from precipitation flows across the surface of the land into lakes, streams, and oceans.