Water cycle · Mochi IsleScience for kids

How does the water cycle work?

In short: The sun turns water from seas and lakes into invisible water vapour. The vapour rises, cools into tiny droplets that form clouds, and falls as rain or snow, which flows back into rivers and the sea, round and round.

How it works

The sun acts like a giant heater. It warms water in seas, lakes and puddles until some of it turns into water vapour, a gas you cannot see. This is called evaporation. The vapour rises with warm air, and plants add even more by giving off water from their leaves.

The higher you go, the colder the air. When water vapour cools, it turns back into very tiny droplets. This is called condensation. Billions of droplets together make a cloud. The droplets bump into each other and join, and when they become too heavy for the cloud to hold, they fall as rain, or as snow if it is cold enough.

Some rain runs into streams and rivers and back to the sea. Some soaks into the ground to become groundwater, or is drunk up by plant roots. Then the sun warms it again and the cycle keeps turning. The water on Earth has been going round this loop for a very, very long time.

Where to see it in New Zealand

The West Coast and Fiordland are among the rainiest places in New Zealand. Moist air from the Tasman Sea hits the Southern Alps and is forced upwards, cooling into thick cloud and heavy rain. After a downpour, many short-lived waterfalls pour down the cliffs of Milford Sound / Piopiotahi.

Try it together

Pour a little water into a bowl and stand an empty cup in the middle. Cover the bowl with cling film and put a coin on top, just above the cup. Leave it in the sun for a few hours. Do droplets form under the film and drip into the cup?

Kids also ask

Is the steam from a kettle water vapour?

Not quite. Real water vapour is invisible, like the clear gap just at the spout. The white cloud you see is made of tiny droplets that formed when the vapour hit cooler air, just like a real cloud.

Will the Earth ever run out of water?

The total amount of water on Earth stays about the same; it just moves between the sea, the sky and the land. But only a small part is clean fresh water we can drink, so it is worth looking after.

In the game, “Water cycle” is a nature card on Mochi Isle.

Your child finds this card by reaching the right place or meeting the right weather on the island, and lights it up by answering the question on the back. Tap the button below and the game shows your child which island it is on and how to find it. Mochi Isle is a browser learning game for ages 5 to 18; the main island and the daily lesson are free.

Find “Water cycle” on the island ↗ All cards from Mochi Isle