What is water?
Water is a clear liquid that covers most of the Earth's surface and fills many of the spaces in and around living things. Its chemical formula is H2O, which means two hydrogen atoms (H) and one oxygen atom (O) join together to form a molecule of water.
Properties of water
- Liquid at most temperatures on Earth: It can flow, take the shape of its container, and form surfaces like oceans and rivers.
- Turns into other states: Water can freeze into a solid (ice) and heat up to become a gas (water vapor).
- Density: Ice is less dense than liquid water, which is why ice floats on water.
- Polar molecule: Water molecules have a slight positive charge on one end and a slight negative charge on the other, helping it dissolve many substances.
States of water
- Solid (ice) — when water gets cold (below 0°C or 32°F). Ice has a rigid structure and floats on liquid water.
- Liquid (water) — at temperatures between 0°C and 100°C (32°F to 212°F). It flows and forms waves and puddles.
- Gas (water vapor) — when water is heated enough to become a gas. Water vapor rises into the air and can cool to form clouds or fog.
Why water matters
- For life: All living things need water to survive, grow, and stay healthy.
- In the environment: Water shapes weather, supports habitats, and helps transport nutrients.
- Everyday uses: We drink it, cook with it, clean with it, and use it in many products and processes.
Simple experiments you can try
- Melting ice: Place ice cubes in a cup at room temperature and watch them melt into liquid water.
- Evaporation: Leave a small amount of water in a tray and observe it slowly disappear as it turns into water vapor.
- Water and ice density: Put a piece of ice in a glass of water to see that it floats.