A Journey through States of Water
Why This Matters
You drink water every day. You see it everywhere. But have you ever stopped and watched it closely?
Think about a glass of cold lemonade on a hot day. There is hard ice floating in it. There is cool water all around the ice. And after some time, tiny drops appear on the outside of the glass. Where did those drops come from?
Or think about a rainy morning. There are puddles of water in the playground. By evening, the puddles are gone. Nobody drank that water. So where did it go?
Here is the surprise. Ice, water, and the wet feeling in the air are all the same thing — water. Water just wears different “costumes”. Sometimes it is hard. Sometimes it flows. Sometimes it floats away into the air where you cannot even see it.
In this chapter, we will follow water on its journey. We will see how it changes from one form to another. And we will answer all those little “but why?” questions. By the end, you will understand rain, dew, drying clothes, and even why an earthen pot keeps water cool.
The Big Idea
Water can take three forms, called states: solid (ice), liquid (water), and gas (water vapour). It is the same substance in all three — only the form changes. Adding heat pushes water towards the gas form (ice melts, water becomes vapour). Cooling pushes it back the other way (vapour becomes drops, water freezes into ice). Water is always travelling between these states, all around us, all the time.
Let’s Break It Down
Three states of water
A state is just a form that water can take. Water has three states.
Let us meet all three. First, a quick word for each one.
- Solid — this is ice. It is hard. You can hold it in your hand. It keeps its own shape.
- Liquid — this is ordinary water. It flows. It takes the shape of whatever you pour it into.
- Gas — this is water vapour. It is water that has floated away into the air. You cannot see it. It spreads out to fill all the space it can.
Figure 8.1 below shows all three side by side, so you can compare them.
Notice one important thing. Water vapour is invisible. The white cloud you see above a kettle or above hot tea is not the gas itself. That white is made of tiny drops of liquid water. The real gas, the water vapour, you cannot see at all. It is floating in the air around you right now.
Let us see how these three behave differently.
| What we check | Solid (ice) | Liquid (water) | Gas (water vapour) |
|---|---|---|---|
| Does it have a fixed shape? | Yes — keeps its own shape | No — takes the shape of the container | No — spreads to fill all the space |
| Can it flow? | No | Yes | Yes, it spreads |
| Can you hold it in your hand? | Yes | No, it slips away | No, you cannot even see it |
Some other things behave like this too, not just water. Wax, oil, and ghee can also be solid or liquid. You may have seen coconut oil turn solid in winter and melt again in summer. So this idea works for many substances.
Steam from a kettle looks white. Is that white thing the water vapour (the gas) itself?
No. Water vapour, the gas, is invisible. The white cloud you see is made of tiny drops of liquid water that formed when the vapour cooled a little. The actual gas you cannot see.
Melting and freezing
How do we change water from one state to another? The trick is heat and cooling.
Take an ice cube out of the freezer and leave it on a table. After some time, it turns into a puddle of water. The ice has changed into liquid.
Melting means a solid changing into a liquid when it gets warmer.
Ice melts into water at 0 °C.
Now go the other way. Put water in the freezer. It gets very cold. After some hours, it becomes hard ice.
Freezing means a liquid changing into a solid when it cools down.
Water freezes into ice at 0 °C too — the same temperature, just going the other way.
So melting and freezing are opposites. Heat melts ice into water. Cooling freezes water into ice.
In fact, all the changes between states follow one simple rule: heat moves water towards gas, and cooling moves it back towards solid. Figure 8.2 below maps out every change with arrows, so you can see the whole picture at once. We will meet the two right-hand changes (evaporation and condensation) in the next sections.
Evaporation — it happens at all temperatures, and it cools things
Remember the puddles that disappeared by evening? Nobody heated them. The sun was not boiling them. Yet the water went away. How?
The water slowly turned into water vapour and floated off into the air. This is evaporation.
Evaporation means a liquid slowly changing into a gas (water vapour) from its surface.
Here is the part that surprises most people. Evaporation does not need boiling. It does not even need a hot day. Wet clothes dry. A mopped floor dries. The sweat on your skin dries. All of this is evaporation, and all of it happens at normal, everyday temperatures. Evaporation is going on quietly, all the time, all around you.
But why does evaporation happen even without heating?
Think of the water as a huge crowd of tiny moving bits. They are not all moving at the same speed. Some bits move slowly. A few bits move very fast. The fastest bits, right at the top surface, have enough speed to jump out of the water and fly off into the air. That escaping is evaporation. Even on a cool day, a few bits are always fast enough to escape.
This also explains a magic trick: evaporation makes things cooler. Figure 8.3 below shows why.
That is exactly why you feel cool when you put sanitiser on your hands, and why sweating cools your body on a hot day. As the liquid evaporates, it carries the heat away with it.
This is also the secret of the matka (earthen pot). Water slowly seeps through the tiny holes in the clay and evaporates from the outside. That evaporation takes heat away from the pot, so the water inside stays cool — without any electricity.
A few things make evaporation faster. Spreading water out gives it more surface for bits to escape from. Heat and sunshine give the bits more speed. And wind blows the escaped vapour away, making room for more to escape. That is why clothes dry faster on a hot, windy day, and slower on a wet rainy day.
A wet floor dries on a cool morning, with no heater on. Is that evaporation?
Yes. Evaporation happens at every temperature, not just on hot days. Even on a cool morning, the fastest bits of water keep escaping into the air, so the floor slowly dries.
Condensation — water drops on a cold glass, dew, and fog
Now back to the mystery of the cold glass. Drops appeared on the outside. The glass did not leak, because the water level inside did not go down. So where did the drops come from?
They came from the air.
Remember, the air around us always has invisible water vapour in it. When this vapour touches a cold surface, it cools down. When it cools, the gas turns back into tiny drops of liquid water. This is condensation.
Condensation means a gas (water vapour) changing back into a liquid when it cools down. It is the opposite of evaporation.
Figure 8.4 below shows exactly how the drops form on a cold glass.
Once you understand this, you can explain many everyday things.
- Dew — On cold nights, leaves and grass get cold. Thin, light things (like a blade of grass) lose their heat and cool down faster than thick, heavy things (like a road), which hold their warmth longer. Water vapour in the air touches the cold grass, cools, and forms little drops. That is why you see dew drops on plants in the early morning. (In Chapter 10, you will see that plants can also push out their own water droplets at the edges of their leaves — that is different from dew, which comes from the air.)
- Fog — Clouds form high up in the sky when the air there cools. Fog is like a cloud that forms right down at ground level. On a clear, cold night the ground gets cold. The air touching the ground cools too, and its water vapour turns into tiny floating drops. That low, misty layer you walk through in the morning is fog.
- Water under the lid — When you boil water with a lid on top, the rising vapour hits the cool lid, condenses, and you see drops on the underside of the lid.
Boiling — and how it differs from evaporation
Heat water on a stove. It gets hotter and hotter. At 100 °C it starts to boil. Big bubbles rise up fast, and lots of vapour escapes.
Boiling is when a liquid turns into gas quickly, throughout the whole liquid, at one fixed temperature (100 °C for water).
Boiling and evaporation both turn water into vapour, but they are not the same. The table below shows the difference.
| Evaporation | Boiling | |
|---|---|---|
| When does it happen? | At any temperature, all the time | Only at one fixed temperature (100 °C for water) |
| Where in the water? | Only at the top surface | All through the water (you see bubbles) |
| How fast? | Slow and quiet | Fast, with bubbles and steam |
| Does it need heating? | No | Yes, strong heating |
So a puddle drying in the sun is evaporation. Water bubbling in a pan is boiling. Both make vapour, but in very different ways.
The water cycle — tying it all together
Now let us put the whole journey together. The water on Earth never sits still. It keeps moving around in a giant loop, again and again. This loop is called the water cycle.
Let us walk through one full round of the journey.
Follow one drop of water on its journey from the ocean and back. What happens at each step?
-
The sun heats the ocean. Water at the surface evaporates. It turns into invisible water vapour and rises up into the air. (This is evaporation — a liquid becoming a gas.)
-
High up, the air is much cooler. The vapour cools down. It condenses into tiny drops, which join together to form clouds. (This is condensation — a gas becoming a liquid.)
-
More and more tiny drops join. They grow into bigger, heavier drops. Soon they are too heavy to float. They fall down as rain. Water falling from the clouds like this has a special name — precipitation. Rain is the most common kind, but in very cold places the water falls instead as snow or as hail (small lumps of ice). Rain, snow and hail are all forms of precipitation.
-
The rain water flows over the land, into streams and rivers. The rivers carry it back to the ocean. Now the drop is back where it started — and the whole cycle begins again. So the journey never ends: evaporation, condensation, rain, flow back, repeat.
Figure 8.5 below shows the whole water cycle in one picture. Follow the numbers 1 to 4.
One last idea: the amount of water vapour in the air has a name. It is called humidity. On a rainy day there is already a lot of vapour in the air, so the air is very humid. When the air is already full of vapour, it is harder for more water to evaporate. That is exactly why clothes dry so slowly on a wet, rainy day.
Common Mistakes
The drops on the outside of a cold glass leaked out from inside the glass.
It feels obvious — the glass is full of water, the outside is wet, so it looks like water sneaked out through the glass.
The drops come from the air, not from inside. The water level inside the glass does not go down at all. Invisible water vapour in the air touches the cold glass, cools, and condenses into drops on the outside.
Evaporation only happens when you heat water.
We usually see vapour rising from hot things — tea, a kettle, a stove — so heating and evaporation seem to always go together.
Evaporation happens at every temperature, all the time. Wet clothes, a mopped floor, and a drying puddle all evaporate without any heating. Heat only makes evaporation faster; it is not needed for it to happen.
The white cloud you see above boiling water or hot tea is water vapour (the gas).
It rises from the hot water and looks like steam, so it is easy to call it the gas itself.
The real water vapour is completely invisible. That white cloud is made of tiny drops of liquid water — vapour that has already cooled a little and condensed. The gas you simply cannot see.
Boiling and evaporation are just two names for the same thing.
Both turn water into vapour, so it is natural to think they are the same process.
They are different. Evaporation is slow, happens only at the surface, and works at any temperature. Boiling is fast, happens all through the water with bubbles, and only at one fixed temperature (100 °C for water).
Quick Check
Tiny drops appear on the outside of a cold cold-drink bottle. Where does this water come from?
Which of these is an example of evaporation?
Why does an earthen pot (matka) keep water cool?
Practice Problems
Easy
Name the three states of water and give the everyday name we use for each.
The three states are:
- Solid — we call it ice.
- Liquid — we call it water.
- Gas — we call it water vapour.
They are all the same substance, just in different forms.
What is the name for each change? (a) Ice turning into water. (b) Water turning into ice.
(a) Ice turning into water is called melting. It happens when the ice warms up to 0 °C.
(b) Water turning into ice is called freezing. It happens when the water cools down to 0 °C.
Melting and freezing are opposites of each other.
Medium
On a rainy day, clothes take a very long time to dry. Explain why, using the idea of humidity.
Drying is evaporation — water leaving the clothes as vapour and going into the air.
But on a rainy day, the air is already full of water vapour. We say the air has high humidity. When the air already holds a lot of vapour, there is little room for more.
So the water in the clothes finds it hard to evaporate into the already-full air. Evaporation slows down, and the clothes dry very slowly.
Both evaporation and boiling turn water into vapour. Write two ways in which they are different.
Here are two clear differences:
-
Temperature. Evaporation happens at any temperature, all the time. Boiling happens only at one fixed temperature (100 °C for water).
-
Where it happens. Evaporation happens only at the top surface of the water, quietly. Boiling happens all through the water, fast, with lots of bubbles.
(Another difference: boiling needs strong heating, but evaporation does not need heating at all.)
Challenge
In the morning you see dew drops on grass, but not on the road nearby. Both were under the same sky all night. Why do drops form on the grass and not on the road?
Dew forms by condensation: water vapour in the air touches a cold surface, cools, and turns into liquid drops. So a surface must get cold enough for this to happen.
Thin blades of grass lose their heat to the night air very quickly. By early morning they become quite cold — cold enough for the vapour touching them to condense into dew drops.
The road is thick and heavy. It holds on to the day’s heat much longer and stays warmer through the night. Because it is not cold enough, the vapour touching it does not condense, so no dew forms.
So the difference is how cold each surface gets. The cold grass triggers condensation; the warmer road does not.
Summary
- Water has three states: solid (ice), liquid (water), and gas (water vapour). They are the same substance in different forms.
- Water vapour is invisible. The white cloud above hot water is tiny liquid drops, not the gas itself.
- Melting = solid to liquid (warming). Freezing = liquid to solid (cooling). Both happen at 0 °C for water.
- Evaporation = liquid slowly becoming vapour. It happens at all temperatures, all the time — not only on heating.
- Evaporation cools things, because the fastest, hottest bits escape and carry heat away (sweat, sanitiser, the matka).
- Condensation = vapour cooling back into liquid drops. It explains drops on a cold glass, dew, and fog.
- Boiling is fast vaporising at one fixed temperature (100 °C), with bubbles — different from quiet, any-temperature evaporation.
- In the water cycle, water evaporates from oceans, condenses into clouds, falls as rain, and flows back — over and over.
What’s Next
We have followed water as it changes form and travels around the Earth. But in real life, water often comes mixed with other things — mud in river water, salt in sea water, husk mixed with grain.
In the next chapter, Methods of Separation in Everyday Life, we will learn the clever ways to separate one thing from a mixture — and you will be surprised how many of these tricks you already use at home every day.
Frequently Asked Questions
What are the three states of water and how do they change into each other?
Water exists as solid (ice), liquid (water) and gas (water vapour). When ice is heated it melts into liquid water at 0 °C. When liquid water is heated to 100 °C it boils and becomes water vapour. When water vapour cools it condenses back into liquid water. When liquid water is cooled to 0 °C it freezes back into ice. The same water keeps changing between these three states again and again.
Why do clothes dry faster on a hot sunny day than on a cloudy day?
Clothes dry by evaporation — water on the cloth turns into invisible water vapour and goes into the air. Evaporation happens faster when the temperature is higher (more heat gives water molecules more energy to escape), when it is windy (wind carries away the water vapour so more can keep evaporating), and when the air is dry (humid air already has a lot of water vapour so evaporation slows down). A sunny, breezy, dry day has all three advantages.
Why do water drops form on the outside of a cold glass?
The air around us always has some invisible water vapour in it. When this warm, moist air touches the cold surface of the glass, it cools down quickly. Cold air cannot hold as much water vapour as warm air, so the extra water vapour turns back into tiny liquid drops on the glass surface. This process is called condensation. The drops come from the air, not from inside the glass.
What is the water cycle class 6?
The water cycle is the continuous journey of water between the Earth and the sky. The Sun heats water in rivers, lakes and oceans, turning it into water vapour that rises into the air (evaporation). High up, the vapour cools and turns into tiny water droplets that form clouds (condensation). When these droplets grow heavy enough they fall as rain or snow (precipitation). The rain flows into rivers and soaks into the ground, and the cycle begins again.
Why does an earthen pot keep water cool in summer?
An earthen pot has millions of tiny pores (holes) in it. Water slowly seeps through these pores to the outside surface of the pot. On the outer surface, this water evaporates. Evaporation absorbs heat from the pot and the water inside it. This removes heat from the water inside, making it cooler. It works on the same idea as sweating — your body cools itself by evaporating water through your skin.