The Water Cycle

The water cycle is the journey water takes between the Earth's surface and the sky, over and over, without ever running out. The sun warms water and it rises as invisible vapour. High up it cools, gathers into clouds, and eventually falls back as rain or snow. Then it collects in rivers, lakes and oceans — and begins again.

It is the reason rain exists, the reason puddles dry up, and the reason the planet has kept roughly the same amount of water for billions of years.

Evaporation: the sun heats water in oceans, lakes and rivers, and it rises into the air as water vapour.

Condensation: as the vapour rises it cools, turning back into tiny liquid droplets that cluster together to form clouds.

Precipitation: droplets in the cloud combine until they are heavy enough to fall as rain, snow, sleet or hail.

Collection: the fallen water gathers in oceans, lakes, rivers and underground — ready to evaporate again.

Two things, and neither ever switches off. The sun supplies the energy that lifts water into the air, and gravity pulls it back down.

Because the sun keeps shining and gravity keeps pulling, the cycle has no end. It is not a process that finishes — it is a loop that has been turning since long before there was anyone to watch it.

The water cycle delivers fresh water to land. Oceans hold most of Earth's water, but it is salty; evaporation leaves the salt behind, so the rain that falls on fields and reservoirs is fresh.

This is what makes farming, drinking water and life on land possible at all. Every river begins as rain that was once seawater.