Earth Watch: Water 3 (RealVideo) This clip explains the stages in the endless water cycle through which all the water available on Earth passes. Learn how water travels throughout our environment in a continuous cycle, falling to Earth as precipitation from clouds, and eventually returns to the sky, evaporating into a gas by heat from the sun. Explore how noxious elements such as mercury become a part of this cycle, and how this can affect all of Earth’s creatures.