Water on Earth is always moving and changing in an endless process called the water cycle. This cycle has been happening for billions of years and is the reason we have fresh water to drink. It starts when the sun heats up water in oceans, lakes, rivers, and even puddles. The heat causes the water to turn into an invisible gas called water vapor that rises into the air. This process is called evaporation.
Water also evaporates from plants through tiny holes in their leaves. As the water vapor rises higher and higher into the atmosphere, it gets colder because the air is cooler up high. When water vapor gets cold enough, it changes back into tiny liquid water droplets. This process is called condensation. Millions and millions of these tiny droplets come together to form clouds that you can see floating in the sky.
The droplets in the clouds bump into each other and stick together, growing bigger and bigger. When the droplets become too heavy to float in the air anymore, they fall back down to Earth. This falling water is called precipitation, and it can happen as rain, snow, sleet, or hail depending on how cold the air is. When precipitation reaches the ground, some of it soaks into the soil where plant roots can use it. The rest flows into streams and rivers, eventually returning to the ocean where the whole amazing cycle begins again.