Water is one of the most important substances on Earth. Most of the Earth's surface is made of water. Most of our bodies are made of water, too. Water keeps our bodies working. It is needed by the crops that become our food. It is a home for fish, crabs, whales, and dolphins.
What makes water so important? Water has special properties. Water is found in many forms on Earth. Water freezes to form ice. Water is heated to form steam. It evaporates into the air to form water vapor. Water is found as a solid, a liquid, and a gas at Earth's normal temperatures. It is the only substance on Earth that is found in all three forms.
As a solid, ice is unique because it will float in water. This is because water expands, or gets bigger, as it freezes. Most liquids get smaller when they freeze. Water is different. Ice cubes float in a glass of water. Icebergs float in the ocean.