The amount of water on Earth stays almost the same. It moves in a continuous loop called the water cycle. The heat of the sun turns water from the seas and rivers into vapor, and the vapor rises into the air. High up, the vapor cools and condenses, and it forms clouds. When the drops inside a cloud become heavy, they fall as rain, snow or hail. Some of this water flows over the ground to the rivers and seas. Another part sinks into the ground and forms groundwater. This happens in every part of the world, at every hour. Then the cycle begins again without a stop.

Question: How does groundwater form, according to the text?