Topics · Primary Science · Cycles: Water Cycle
The water cycle
The same water goes round for ever: up from the sea as vapour, down as rain, back to the sea. No water is made and none is lost — which is why it is drawn as a ring.
- 237 exam papers analysed
- appears in 76% of P6 Science papers
- ~3 min read
01 The four stages
Heat from the sun drives the whole thing. Take the sun away and the cycle stops.
- Evaporation — the sun heats water in seas, rivers and lakes, and it becomes water vapour, an invisible gas.
- Condensation — the vapour rises, cools high up, and turns back into tiny droplets, which is what a cloud is.
- Precipitation — the droplets join, get heavy, and fall as rain, snow or hail.
- Collection — the water gathers in seas, rivers, lakes and the ground, ready to evaporate again.
02 What a cloud actually is
A cloud is tiny liquid water droplets, not gas. Water vapour is invisible; you cannot see it.
So the white cloud above a kettle is not steam either — it is droplets that have already condensed in the cooler air.
Clouds form because air is colder higher up. Condensation always needs cooling, and that is the one-word answer to why clouds form where they do.
03 Plants are part of it
Water also leaves plants through their leaves, as transpiration. It joins the same cycle.
So a forest returns a great deal of water to the air, and cutting one down reduces how much goes back up — the standard link between this topic and the environment.
Water also soaks into the ground and travels underground to rivers and the sea, which is part of the collection stage rather than a separate one.
04 Nothing is created or lost
The total amount of water on Earth stays the same. The water in a glass today has been round the cycle countless times.
That is why questions ask what happens if one stage stops. No sun — no evaporation, so no clouds and no rain. Air that never cools — no condensation, so no rain even with plenty of vapour.
Work along the ring and say what is cut off after the missing stage; the stages before it carry on as normal.
05 How to say them
These are words most children have never said out loud, and a word you cannot say is a word you avoid using. Capitals mark the syllable you lean on. Tap the speaker to hear it.
- evaporationsayi-vap-uh-RAY-shuhn
Liquid water becoming water vapour, driven by heat from the sun.
- condensationsaykon-den-SAY-shuhn
Water vapour cooling and becoming liquid droplets. This is how clouds form.
- precipitationsaypri-sip-i-TAY-shuhn
Water falling from clouds as rain, snow or hail.
- water vapoursayVAY-puh
Water as a gas. Invisible — a cloud is droplets, not vapour.
- transpirationsaytran-spi-RAY-shuhn
Water leaving plants through their leaves, joining the water cycle.
06 What each level is tested on
The same topic, asked differently as it goes up. The percentage is the share of papers at that level in which it appears.
- P5
The four stages, what drives them, and what a cloud is.
Practise P5 Cycles: Water Cycle — 10 questions →72% of P5 papers
- P6
The cycle in longer questions, transpiration's part in it, and what happens if a stage is interrupted.
Practise P6 Cycles: Water Cycle — 9 questions →76% of P6 papers
07 Mistakes worth knowing about
Each of these is wrong. Decide why before you open it.
“Clouds are made of water vapour.”
Vapour is invisible. A cloud is tiny liquid droplets that have already condensed.
“New water is made when it rains.”
The same water goes round for ever. The total on Earth does not change.
“Water evaporates because it is windy.”
Heat from the sun drives evaporation. Wind speeds it up but is not the cause.
“Only the sea evaporates.”
Rivers, lakes, puddles, wet ground and plants all return water to the air.
“Clouds form because the air gets warmer.”
Condensation needs cooling. Air is colder higher up, which is why clouds form there.
Now try it
19 questions across 2 levels, marked as you go with the working shown.