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The water on Earth is always moving between the oceans, the air and the land. This never-ending journey is the water cycle. It is powered by energy from the Sun and by gravity.

Evaporation changes liquid water into a gas, water vapour. Heat from the Sun makes water evaporate from oceans, lakes and the ground. Plants also release water vapour through their leaves: this is called transpiration. About 90% of the water in the air comes from evaporation and about 10% from transpiration.

As air rises, it cools. In the cooler air higher up, some of the water vapour turns back into tiny liquid droplets. This is condensation, and it forms clouds.

Experiment: Fair test: what makes water evaporate faster?

1. Put exactly the same amount of water (for example 50 ml) in each dish.
2. Choose ONE thing to change: put two dishes in a warm, sunny place and two in a cool, shady place.
3. Keep everything else the same: same dishes, same amount of water, same start time, no lids.
4. Predict which dishes will lose water fastest.
5. Each day at the same time, measure the depth of water with a ruler (or pour it into the jug to measure).
6. Compare the results. Was your prediction right?

Dish	Place	Start (ml or mm)	Day 1	Day 2	Day 3
A	I think the water will disappear fastest in the … place, because …
B	I think the water will disappear fastest in the … place, because …
C	I think the water will disappear fastest in the … place, because …
D	I think the water will disappear fastest in the … place, because …

Questions

1. Draw and label the water cycle with the words: evaporation, condensation, precipitation, runoff.

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2. Explain why clouds form high up in the sky.

3. In your fair test, what did you change, what did you measure and what did you keep the same?

4. Over 96% of Earth's water is in the oceans. Why can't we simply drink sea water?

Sources for every fact on this sheet: echoesof.science/school/water-cycle/sources/

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