The water cycle — Geography, 11–13 years
Water is always moving between the ground, the air, rivers, seas and living things. The water cycle links these places and explains why rain, clouds and flowing water are connected.
Water keeps changing place
The Sun warms water, and some of it becomes invisible water vapour. The vapour rises, cools and forms tiny drops in clouds; later, water falls as rain or snow. It may soak into soil, flow to a river or return to the air from plants and open water.
Why follow the water?
People need to know where water comes from, where it goes and how quickly it returns. This matters when planning drinking-water supplies, farms or flood protection. The cycle is a model for tracking water, not a perfect loop that takes the same time everywhere.
A drop over a town
Imagine one drop in the sea. Step 1: sunlight warms it and it evaporates. Step 2: the vapour cools into a cloud. Step 3: the drop falls as rain on a hill. Step 4: it runs into a stream, then a river, and finally returns to the sea, ready to begin again.
The trap: water does not vanish
When a puddle dries, it can look as if the water has disappeared. In fact, its molecules have changed into vapour and mixed with the air, so our eyes can no longer see them. The same idea explains why wet clothes dry, even though no water seems to fall away.
Water in real decisions
A town planning a new reservoir studies rainfall, rivers, underground water and evaporation. Farmers use the same thinking to decide when irrigation may be needed. In a city, paving over soil can reduce soaking-in and make rainwater run away faster, increasing flood risk.
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