Water moves through the nonliving parts of an ecosystem during the water cycle through the process of evaporation. This is when water changes from a liquid to a gas due to the sun's heat energy. Once the water vapor is in the air, it can travel great distances before it condenses back into a liquid, forming clouds. Eventually, the water droplets in the clouds fall back to the Earth's surface as precipitation, which can take the form of rain, snow, hail, or sleet. This water can then enter streams, rivers, lakes, and oceans, and the cycle begins again.