Where does rain come from?

The longer answer

There is always some water in the air around us, even on a sunny day. We cannot see it because it is a gas, spread out too thin to see.

When that air cools down, the water turns back into drops. Scientists call it condensation. It is the same thing that happens on the outside of a glass of ice water: the cold glass cools the air touching it, and drops appear on the outside as if from nowhere.

The rain runs into rivers and back to the sea, the Sun warms it again, and the trip starts over. That loop is called the water cycle, and the same water has been going round it for millions of years.

Three things to know

• Clouds are made of tiny water drops floating in the air. The drops are so small and light that the air holds them up, until they bump together and grow heavy enough to fall.
• The same water goes round and round, from sea to sky to rain. Water never gets used up. The water in your glass has been on that trip many, many times.
• Your breath makes a cloud on a cold day. Warm breath carries water. When it meets cold air, the water cools into tiny drops you can see, just like a cloud.

Try it at home: Make rain on a glass

1. Fill one glass with ice water and another with water from the faucet.
2. Dry the outside of both glasses and stand them side by side.
3. Wait a little while, then touch the outside of each glass.
4. Which glass got wet on the outside? Where did that water come from?

On a cold morning, breathe onto a window and watch your own little cloud appear and fade.