Ocean
https://www.bing.com/images/search?q=ocean%20&qs=n&form=QBIR&sp=-1&pq=ocean%20&sc=8-6&sk=&cvid=D928B7CF1ACC4227832F80723572046B

You may be familiar with how water is always cycling around, through, and above the Earth, continually changing from liquid water to water vapor to ice. One way to envision the water cycle is to follow a drop of water around as it moves on its way. I could really begin this story anywhere along the cycle, but I think the ocean is the best place to start, since that is where most of Earth’s water is.