The water cycle — Science, 7–10 years
Water travels between the ground, air, rivers, lakes and seas. Sunlight and cooling keep moving it through evaporation, condensation and precipitation.
Water keeps moving
The water cycle is water changing place and sometimes changing state. Sunlight warms water so some becomes invisible vapour. Higher, cooler air can turn vapour into tiny drops in clouds. When drops grow heavy, water falls as rain, snow or hail and starts the journey again.
Why describe a cycle?
A puddle can disappear, yet water has not simply stopped existing. Scientists needed a way to connect puddles, clouds, rivers and rain. The cycle explains where water goes and why the same water can be used again and again, although it may travel far or stay frozen for a while.
A puddle after rain
Imagine a puddle left after rain. First, the Sun warms its surface, and some water evaporates into the air. The vapour rises and cools, then forms tiny drops in a cloud. Later, the drops join and fall as rain. Some runs into a stream, while some soaks into the ground.
Clouds are not made of smoke
A cloud can look like a soft white object floating in the sky, so it is easy to imagine it as smoke or mist that stays together. In fact, a cloud contains countless tiny water drops or ice crystals. They are light enough to remain in moving air, but can join and fall as precipitation.
Planning for water
Farmers watch rainfall and soil moisture to decide when crops need water. Towns collect, clean and store water because rain does not fall everywhere at the same time. Understanding the cycle helps people protect supplies, but it does not make fresh water unlimited or remove the need to use it carefully.
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