What is the water cycle?
The water cycle describes the continuous movement of water between lakes, rivers, oceans, and the atmosphere.
During this cycle, water can be in the form of a solid (ice), liquid (water) or gas (vapour).
It might be hard to imagine, but the water you drink today is the same water that would have been used by ancient civilisations and even the dinosaurs! That's because the water cycle continuously recycles the Earth's water supply.
What are the four stages of the water cycle?
One type of energy can change into another type of energy. Energy transformation means the changing of energy from one type to another, e.g. from kinetic energy to electrical energy, or from potential energy to kinetic energy.
1. Evaporation: As the Earth's surface is heated by the Sun, the temperature of the rivers, lakes, and oceans rises. This causes some of the water to evaporate into the atmosphere, where it turns into a gas called vapour.
Plants also lose water to the atmosphere through their leaves, in a process called transpiration.
2. Condensation: As the water vapour rises, it cools – this makes it turn back into a liquid, which forms clouds. This process is called condensation. Clouds are moved around the Earth by currents high up in the sky.
3. Precipitation: When the water droplets in the clouds become too large and heavy for the air to hold, they fall back down to Earth. This is called precipitation – and that's how we get rain, snow, hail or sleet!
4. Collection: The fallen water will be collected by rivers, lakes, and oceans, ready for the cycle to begin again. How it ends up back in these bodies of water depends on where it lands:
It may land directly in a river, lake or ocean
It may land on vegetation and evaporate back into the air, or be taken up by plant roots
In cold climates, it may build up over time on the land as snow, ice or glaciers – when the frozen water melts, it will soak into the ground or flow into rivers, lakes, or oceans
It may land on the ground and flow across the Earth until it reaches a river, lake or ocean – this water is called surface run-off
