Water Cycle Water can exist either as a solid (ice), a liquid (water), or a gas (water vapor). Water on the on surface of Earth is constantly changing between these three states. Ice can change to become water or water vapor. Water can change to become ice or water vapor. Water vapor can change to become ice or water. These continuous changes in state create a cycle of repeating events. Water continually circulates between the surface of Earth and its atmosphere in what is called the hydrologic or water cycle.