The Amazing World of Water

The Most Important Liquid on Earth

Take a sip of water. It has no colour, no smell and almost no taste. It seems like the simplest, most ordinary thing in the world. And yet water is one of the most amazing substances in the entire universe.

Without water, there would be no fish, no trees, no birds, no people — nothing alive at all. Water fills the oceans, falls from the sky as rain, floats above us as clouds, and flows quietly inside your own body. In fact, more than half of you is made of water! This book is the story of that incredible liquid and all the surprising things it can do.

Three Forms in One

One of the most magical things about water is that it can change its shape and form. Water can be a solid, a liquid or a gas, and it can switch between them again and again.

When water gets very cold, it freezes into a hard solid called ice. Ice is what you find in snowflakes, in frozen ponds, and in the ice cubes in a glass.

When ice warms up, it melts back into a liquid — the wet, runny water you drink and swim in. Liquid water flows downhill, takes the shape of any cup or bowl, and splashes when you jump in a puddle.

If you heat water even more, it turns into an invisible gas called water vapour. You can see this happening when steam rises off a hot bath or a boiling pot. The steam is made of tiny droplets of water floating in the air.

The wonderful part is that it is always the same water. Freeze it, melt it, boil it — it is still water, just wearing a different costume.

The Water Cycle: Nature's Greatest Journey

Here is a question that has puzzled people for thousands of years. If rivers are always flowing into the sea, why don't they run dry? And if rain keeps falling, why doesn't the world flood?

The answer is one of the greatest ideas in all of science: the water cycle. Water never disappears. Instead, it travels around the planet in an endless loop, going round and round forever.

Let's follow a single drop of water on its journey:

1. The Sun warms the surface of the ocean. Some of the water turns into water vapour and floats up into the sky. This is called evaporation.
2. High in the cool air, the vapour turns back into tiny droplets that gather together to make a cloud. This is called condensation.
3. When a cloud holds too much water, the drops fall back down as rain, or as snow if it is very cold. This is called precipitation.
4. The rain runs into streams and rivers, which carry the water all the way back to the sea — and the journey begins again.

The very same water has been making this trip for billions of years. The water in your glass today might once have been a snowflake on a mountain, a wave in the ocean, or even a drink for a dinosaur!

Why Living Things Need Water

Every plant and animal on Earth needs water to stay alive. But why?

Inside your body, water does a hundred important jobs. It carries food and energy to every part of you through your blood. It helps you cool down when you sweat on a hot day. It carries away waste your body doesn't need. Without enough water, your body simply cannot work — which is why you feel thirsty. Thirst is your body's clever way of saying, "Please, I need more water!"

Plants drink water too. They pull it up from the soil through their roots, all the way to their leaves, where they use it to make their food using sunlight. A wilting, droopy plant is a thirsty plant. Give it a drink and watch it perk up again.

Animals find water wherever they can — at rivers, ponds and waterholes. Some desert animals are so good at saving water that they can go for a long time without drinking at all, getting most of what they need from their food.

Salty Seas and Fresh Water

Look at a globe and you'll see that most of Earth is covered in blue. That is water — so much of it that our planet is sometimes called the "Blue Planet." But there is a catch.

Most of that water is salty seawater in the oceans. We cannot drink it, because the salt would make us ill. Only a small slice of Earth's water is fresh water — the kind we can drink and water our crops with. And much of that fresh water is locked away as ice in cold places, or hidden deep underground.

So the clean, fresh water we use every day is actually quite rare and precious. That is why it is so important not to waste it. Turning off the tap while you brush your teeth, fixing dripping taps, and not leaving water running all save this precious liquid for everyone.

Water Is Powerful

Water may feel gentle when you splash in a bath, but over time it is one of the most powerful forces on Earth. Slowly, drip by drip and wave by wave, water can carve out enormous canyons, smooth rough rocks into round pebbles, and shape entire coastlines.

Rushing rivers can move boulders. Ocean waves can wear away cliffs. Even the gentle freezing of water inside a crack can split a giant rock in two, because water actually grows bigger when it freezes. Given enough time, soft water can defeat the hardest stone. The Grand Canyon, deep enough to swallow tall buildings, was carved out by a single river patiently flowing for millions of years.

What We Learned

Water is the most important liquid on Earth. It can be a solid, a liquid or a gas, and it travels endlessly around the planet in the water cycle, never disappearing. Every living thing — including you — needs water to survive. Fresh, clean water is rare and precious, so it is worth protecting. Simple, ordinary, amazing water is truly the liquid of life.

To explore where so much of Earth's water lives, dive into Explorers of the Deep Sea. Or learn how water in the sky becomes storms in My First Book of Weather.