ScienceThe water cycle
How the same water goes round and round between sea, sky and land.
The water you drank this morning may once have been in the sea, in a cloud, in a river and even in a dinosaur. The earth has had almost the same water for millions of years. It simply keeps moving from the land and sea to the sky and back again. This never-ending journey is called the water cycle.
Step 1: Evaporation
The sun heats the water in seas, rivers, lakes and ponds. Some of the water turns into an invisible gas called water vapour and rises into the air. This change from liquid to gas is called evaporation. Wet clothes dry on a line for the same reason. Plants also give out water vapour through their leaves; this is called transpiration.
Step 2: Condensation
As the water vapour rises, it reaches cooler air. Cooling changes the vapour back into very tiny drops of water. This change from gas to liquid is called condensation. Millions of these tiny drops, floating together around specks of dust, form a cloud. You see condensation at home when drops form on the outside of a cold glass of water.
Step 3: Precipitation
Inside a cloud, the tiny drops join to make bigger drops. When they become too heavy to float, they fall to the earth. Water falling from clouds in any form is called precipitation. It may fall as rain, or as snow or hail when the air is very cold.
Step 4: Collection
The fallen water has to go somewhere. Some of it flows over the land into streams and rivers and finally reaches the sea. This flow is called run-off. Some of it soaks into the soil and collects under the ground; this groundwater is what comes out of wells and hand pumps. Some stays as snow on high mountains and melts slowly to feed rivers. Then the sun heats the water once more, and the cycle begins again.
Why the water cycle matters
- It brings fresh water to the land. Sea water is salty, but when it evaporates the salt is left behind, so rain is fresh.
- It fills rivers, lakes and wells, on which farming and all life depend.
- It moves heat around the earth and shapes our weather.
The amount of fresh water we can use is small. Polluting rivers or wasting water breaks into this cycle, which is why saving water is so important.
Key terms
- Evaporation
- liquid water changing into water vapour
- Condensation
- water vapour changing back into liquid drops
- Precipitation
- water falling from clouds as rain, snow or hail
- Transpiration
- loss of water vapour from the leaves of plants
- Groundwater
- water stored under the ground
Try it yourself
Put a little water in a steel plate and mark the level. Keep it in the sun for a day and look again: some water has evaporated. Now take a glass of ice-cold water and watch drops form outside it within minutes. That is condensation.
Quick questions
Answer in your head or on paper first, then tap to check.
Name the four main steps of the water cycle.
Evaporation, condensation, precipitation and collection.
What is a cloud made of?
Millions of tiny drops of water (or ice) floating in the air.
Why is rainwater not salty even though it comes from the sea?
When sea water evaporates, the salt is left behind.
What is groundwater?
Water that has soaked into the soil and collected under the ground.
This is a simple explanation to help you understand. For examinations, read the same chapter in your prescribed textbook. Last checked: 11 November 2026.