The Water Cycle
Discover how water moves around our planet through evaporation, condensation, precipitation, and collection -- a never-ending journey!
What Is the Water Cycle?
The water cycle (also called the hydrological cycle) describes how water continuously moves between the Earth's surface, the atmosphere, and back again. The same water that dinosaurs drank millions of years ago is still being recycled today!
The Four Main Stages
1. Evaporation
The Sun heats water in oceans, rivers, and lakes. Water turns from liquid into water vapour (gas) and rises into the air.
2. Condensation
As water vapour rises and cools, it turns back into tiny water droplets. These droplets form clouds.
3. Precipitation
When clouds hold too much water, it falls back to Earth as rain, hail, sleet, or snow.
4. Collection
Water collects in oceans, rivers, lakes, and underground. Then the cycle starts all over again!
Amazing fact: About 97% of Earth's water is salty ocean water. Only about 3% is fresh water, and most of that is frozen in ice caps and glaciers!
The Stages in Detail
Evaporation
Heat energy from the Sun causes water molecules to move faster and escape into the air as invisible water vapour.
- ●Happens fastest on hot, dry, windy days
- ●Occurs from oceans, rivers, puddles, and even wet clothes on the line
- ●Transpiration is when plants release water vapour from their leaves
Condensation
When warm water vapour rises high into the atmosphere, it cools and changes back into tiny liquid water droplets.
- ●Billions of tiny droplets clump together to form clouds
- ●You can see condensation on a cold glass of water on a hot day
- ●Fog and dew are also formed by condensation
Precipitation
When water droplets in clouds join together and become too heavy, they fall back to Earth.
- ●Rain -- liquid water falling from clouds
- ●Snow -- frozen water crystals (common in the Australian Alps)
- ●Hail -- balls of ice (sometimes seen in Australian storms)
Collection
After precipitation, water gathers in different places on and below the Earth's surface.
- ●Run-off: Water flows over land into creeks, rivers, and eventually the ocean
- ●Groundwater: Some water soaks into the soil and is stored underground
- ●Lakes and dams collect water for people, animals, and farming
The Water Cycle in Australia
Australia is the driest inhabited continent on Earth. Understanding the water cycle helps us know why water is so precious here.
High Evaporation
Australia's hot climate means lots of evaporation. Lake Eyre in South Australia often dries up completely.
Uneven Rainfall
Northern Australia gets heavy monsoon rains, while central Australia is very dry (the Outback).
Water Storage
We rely on dams, reservoirs, and the Great Artesian Basin (underground water) to store water for dry times.
Think about it: Why do you think water restrictions are sometimes needed during drought? How does the water cycle explain why some years have more rain than others?
Key Vocabulary
Evaporation
The process where liquid water is heated and changes into water vapour (a gas).
Condensation
The process where water vapour cools and turns back into tiny liquid water droplets, forming clouds.
Precipitation
Water falling from clouds to Earth as rain, snow, hail, or sleet.
Transpiration
The process where plants release water vapour through tiny pores in their leaves.
Worked Examples
You leave a glass of water on a windowsill on a hot day. After a few hours, there is less water. What happened?
Step 1: The Sun heated the water in the glass.
Step 2: Some water molecules gained enough energy to escape into the air as water vapour.
Answer: The water evaporated. It turned from a liquid into an invisible gas (water vapour) and went into the air.
Why do clouds form high up in the sky and not near the ground?
Step 1: Water vapour rises because warm air is lighter than cool air.
Step 2: High up in the atmosphere, the air is much cooler.
Answer: The water vapour condenses (turns back into tiny water droplets) when it reaches the cool air high up. These droplets form clouds.
After heavy rain, where does all the water go?
Step 1: Some water flows over the land surface as run-off into creeks, rivers, and eventually the ocean.
Step 2: Some water soaks into the ground and becomes groundwater.
Answer: This is the collection stage. Water is gathered in rivers, lakes, oceans, and underground, ready for the cycle to begin again.
Knowledge Check
Select the correct answer for each question. Click "Check Answer" to see if you are right.
Question 1
What provides the energy that drives the water cycle?
Question 2
When water vapour cools and turns into tiny water droplets that form clouds, this is called:
Question 3
Which of these is an example of precipitation?
Question 4
What is transpiration?
Question 5
Why is Australia's water cycle important to understand?
Key Concepts Summary
- ●The water cycle has four main stages: evaporation, condensation, precipitation, and collection.
- ●The Sun provides the energy that drives the water cycle by heating water and causing evaporation.
- ●Transpiration is when plants release water vapour, adding to the cycle.
- ●Australia is the driest inhabited continent, making water conservation very important.
- ●The water cycle is continuous -- the same water is recycled over and over again.