The Water Cycle
In 2019, Australia's Bureau of Meteorology recorded the driest year in national history, total rainfall was 40% below the long-term average. Yet just one year later, flooding hit eastern Australia repeatedly. Same water, same cycle. In this lesson you'll learn the six key processes of the water cycle and discover why less than 0.3% of Earth's water is ever accessible to us.
Printable Worksheets
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Q1 · Water that falls as rain on the Blue Mountains might end up in a Sydney tap, an underground aquifer, the Murray River, or back in the ocean. Map that journey.
Q2 · Australia has the world's most variable rainfall. Which part of the water cycle do you think is most important for Australian water security?
● Know
- The six processes of the water cycle: evaporation, transpiration, condensation, precipitation, infiltration, runoff
- That only ~0.3% of Earth's water is accessible freshwater
- Key Australian water management strategies: dams, desalination, recycled water
● Understand
- Why Australia is the driest inhabited continent yet cannot "run out" of water
- How the Murray-Darling Basin supports 40% of Australian agriculture
- How climate change affects evaporation and rainfall patterns
● Can do
- Trace a water molecule through the water cycle naming at least four processes
- Describe the difference between infiltration and runoff
- Evaluate the environmental impact of a water management strategy
When liquid water is heated by the sun it becomes water vapour, this is . Water vapour released by plants is called . When water vapour cools it becomes tiny droplets, forming clouds, this is .
Pour a glass of water. The molecules in that glass have already cycled through the atmosphere as rain, frozen into Antarctic glaciers, flowed through rivers, and evaporated from the ocean, millions of times over billions of years. Water doesn't get used up, it cycles endlessly through six key processes.
| # | Process | What happens | Energy involved |
|---|---|---|---|
| 1 | Evaporation | Liquid water → water vapour, from ocean/lake/river/soil surfaces | Solar energy absorbed |
| 2 | Transpiration | Plants release water vapour through leaf stomata | Solar energy (photosynthesis byproduct) |
| 3 | Condensation | Water vapour cools → tiny liquid droplets → clouds and fog form | Heat released |
| 4 | Precipitation | Droplets grow heavy → fall as rain, snow, sleet or hail | Gravity |
| 5 | Infiltration | Water soaks into soil and rock → replenishes groundwater aquifers | Gravity |
| 6 | Runoff | Water flows over land surface → into rivers, lakes, sea | Gravity |
Evapotranspiration: evaporation + transpiration combined, the total water vapour entering the atmosphere from land surfaces.
- Evaporation + transpiration = evapotranspiration (water vapour from land to atmosphere).
- After condensation → clouds → precipitation → either infiltration or runoff.
- The cycle is powered by solar energy (evaporation) and gravity (precipitation, runoff).
After precipitation, water either into the soil to replenish aquifers, or flows over the land surface as into rivers. Both processes are driven by . The whole water cycle is ultimately powered by .
There is plenty of water on Earth, but almost none of it is in the right form in the right place.
| Category | % of total water | Location |
|---|---|---|
| Salt water | 97.5% | Oceans and seas, undrinkable without treatment |
| Ice/glaciers | ~1.7% | Antarctic ice sheet, Greenland, mountain glaciers |
| Groundwater | ~0.76% | Underground aquifers, accessible by drilling |
| Surface freshwater | ~0.013% | Rivers, lakes, wetlands, directly accessible |
Australian context: Australia is the world's driest inhabited continent. Average annual rainfall is about 470 mm (compared to the global average of ~800 mm). Rainfall is highly variable, northern Australia has a pronounced wet season while the interior averages under 200 mm/year.
Water security strategies:
- Dams: store rainfall and river water (e.g. Snowy Mountains Scheme, also generates hydroelectric power).
- Desalination: removes salt from seawater → Sydney, Melbourne, Perth and Adelaide all have desalination plants. Energy-intensive but drought-proof.
- Recycled water: treated sewage water reused for irrigation, industry, and some drinking water schemes.
- Groundwater extraction: from the Great Artesian Basin (covers 22% of Australia).
The Murray-Darling Basin is Australia's most important river system. It covers 1 million km² across four states (QLD, NSW, VIC, SA) and provides water for 3.2 million people and 40% of Australia's agricultural production. Fed by rainfall and snowmelt from the Great Dividing Range.
Threats: drought, over-extraction for irrigation (cotton, rice, fruit), salt buildup, blue-green algal blooms, reduced environmental flows. The Murray-Darling Basin Plan aims to return water to the environment, though it is politically controversial.
Indigenous connection: The Murray-Darling rivers are central to the cultural, spiritual and physical lives of Ngarrindjeri, Yorta Yorta, Wiradjuri and many other First Nations, among the world's oldest continuously managed river systems, tended for at least 60,000 years.
Water cycle and climate change: A warmer climate increases evaporation rates → more intense but less frequent rainfall events → longer dry periods between rain → drier conditions in southern Australia. The Millennium Drought (2001–2009) severely affected the Murray-Darling, and climate projections suggest such droughts will become more frequent.
Australia's average annual rainfall is about 470 mm, but average annual evaporation potential is about 2,000 mm, about 4× more evaporation than rainfall. Predict: does this mean Australia is constantly losing water and will eventually run dry? What balances this equation?
How close was your prediction?
Great, you understood that evaporation is part of the cycle, not a loss from the system.
Key idea: water can't "escape" Earth, evaporation just moves it into the atmosphere where it will eventually condense and fall again somewhere.
At the start of the lesson, you read that less than 0.3% of all water on Earth is accessible freshwater in rivers and lakes, yet all land life depends on it.
Now that you've mapped the full water cycle, explain where the other 99.7% of water is stored, and describe one process that moves water from those vast stores back into accessible freshwater. Use at least two process names from the lesson.
Q1. Describe the water cycle by tracing a single water molecule from the ocean to your school tap. Name at least four processes in your description. (4 marks)
Q2. Why is it incorrect to say that Australia is "running out of water"? Explain using the law of conservation of matter and the water cycle. (3 marks)
Q3. Describe two ways Australians manage water scarcity in cities. Evaluate the environmental impact of one of these methods. (4 marks)
Answers
▾MCQ 1
B Transpiration is specifically the release of water vapour by plants through leaf stomata, not evaporation from open water surfaces.
MCQ 2
C Less than 0.3% of all water is accessible surface freshwater (rivers, lakes). 97.5% is saltwater, most of the remaining 2.5% is locked in glaciers or underground.
MCQ 3
B Condensation is when water vapour cools and forms tiny liquid droplets, making clouds and fog. Rain (precipitation) comes after condensation, when droplets grow heavy enough to fall.
MCQ 4
B The Murray-Darling Basin covers 1 million km² and provides water for 40% of Australian agricultural output, making it the nation's most economically important river system.
MCQ 5
C Higher temperatures increase evaporation from soils and water bodies. This draws more moisture from the landscape, leading to more intense droughts in southern Australia. Warmer air also holds more water vapour, making rainfall more intense but less frequent when it does come.
Short Answer 1
Model answer: A water molecule in the Pacific Ocean is heated by the sun → evaporation turns it to water vapour. It rises, cools, and undergoes condensation → forming a cloud droplet. The droplet grows heavy and precipitation sends it falling as rain over the Blue Mountains. It infiltrates into the soil → enters a groundwater aquifer → is pumped to the surface, treated, and piped to your school tap. Four processes used: evaporation, condensation, precipitation, infiltration.
Short Answer 2
Model answer: It is incorrect because water cannot be created or destroyed, the law of conservation of matter states that matter cannot be lost from a system, only change form. The water cycle continuously redistributes water between the ocean, atmosphere, land, and groundwater. When water evaporates from land it enters the atmosphere and eventually falls as precipitation elsewhere. Australia might experience regional water shortages, but Earth's total water supply stays constant. The issue is not quantity but distribution and access.
Short Answer 3
Model answer: (1) Desalination: seawater is filtered and salt removed to produce drinking water. (2) Recycled water: treated sewage water is reused for irrigation and some industrial processes. Environmental evaluation of desalination: desalination is energy-intensive, typically using fossil fuels or electricity from the grid → greenhouse gas emissions. The brine (concentrated salt) discharge back into the ocean can affect local marine life if not carefully managed. On the positive side, it is drought-proof (doesn't depend on rainfall) and reduces pressure on natural river systems.