Seventy percent of the Earth is covered by water. Warmed by the sun's energy, water from the ocean, lakes, rivers and the earth's surface evaporate into the atmosphere. Evaporation is when water changes from its liquid state into a vapor. Small amounts of water vapor also come from plants that release water through their leaves and from humans and animals when they breathe. As water evaporates from the oceans, it enters the atmosphere and collects on small particles in the air as droplets or ice, a process called condensation, and forms clouds.
Condensation is when a gas, such as water vapor, changes into liquid, such as water.
When enough water or ice collects in a cloud, it rains. If the temperature is low enough, it snows. Snow usually stays on top of the ground until it melts, then it turns into water and runs into streams and rivers. Some of the water from melted snow also goes into the ground for plants and people to drink. Most of the water that falls on land either evaporates in the sun, soaks into the soil or runs off the land back into our lakes or rivers where it may travel for a few days or weeks before flowing out to sea.