Cycles Water on earth is always changing. Its changes make a cycle, or a repeating event. Ice can change to become water and water vapor. Water can change to become ice and water vapor.
Water vapor can change to become ice and water.
Adding heat or subtracting heat makes the cycle work. If I add heat to ice, it melts. If I take heat away from liquid water, it freezes to become ice. The water vapor condenses to form clouds, which are millions of tiny drops. The clouds lose their water as rain or snow.