Learning objectives
- Explain the four main stages of the water cycle.
- Distinguish evaporation from condensation.
- Connect clouds and rainfall to changes of state.
- Identify practical ways to conserve water.
How water moves through nature
The water cycle is the continuous movement of water between Earth’s surface and the atmosphere. Solar energy warms water in oceans, rivers, lakes and wet soil. Some of that liquid water changes into water vapour and rises into the air.
Higher in the atmosphere, the air is cooler. Water vapour loses heat and condenses into tiny droplets. Large groups of droplets form clouds. When droplets combine and become heavy, water returns to the ground as rain, snow or hail.
Collection, runoff and groundwater
After precipitation, some water flows across the surface as runoff and enters streams, rivers and lakes. Some soaks into the soil. Water that moves deeper through soil and rock becomes groundwater.
Plants also return water vapour to the atmosphere through transpiration. Their roots absorb water from soil, and tiny openings in leaves release some of it as vapour.
Why conservation matters
The total amount of water on Earth is large, but only a small part is easily available as clean fresh water. Leaking taps, polluted water bodies and unnecessary use reduce the amount available for people, farms and ecosystems.
Simple actions such as repairing leaks, using a bucket instead of a running hose, collecting rainwater and reusing suitable water can reduce waste.
Practice questions with explanations
Try each question before opening the answer. The explanation shows the reasoning, not only the final response.
Q1. What provides most of the energy that drives the water cycle?
Answer: The Sun.
Explanation: Solar energy heats surface water and causes evaporation.
Q2. What is evaporation?
Answer: The change of liquid water into water vapour.
Explanation: It occurs when water molecules gain enough energy to escape into the air.
Q3. What is condensation?
Answer: The change of water vapour into liquid droplets.
Explanation: Cooling removes energy from vapour, allowing droplets to form.
Q4. Why do clouds form?
Answer: Water vapour cools and condenses around tiny particles in the air.
Explanation: The resulting droplets or ice crystals gather into visible clouds.
Q5. What is precipitation?
Answer: Water falling from clouds as rain, snow, sleet or hail.
Explanation: It happens when droplets or ice crystals become too heavy to remain suspended.
Q6. What is runoff?
Answer: Water flowing over the land surface.
Explanation: Runoff carries water toward streams, rivers, lakes and oceans.
Q7. How is groundwater formed?
Answer: Water infiltrates soil and moves into spaces in rock.
Explanation: This stored underground water can supply wells and springs.
Q8. What is transpiration?
Answer: The release of water vapour from plant leaves.
Explanation: Plants absorb water through roots and release part of it through leaf openings.
Q9. Why can wet clothes dry on a cloudy day?
Answer: Evaporation can still occur without direct sunshine.
Explanation: Air movement and available heat allow water molecules to escape from the cloth.
Q10. Give two practical ways to conserve water at home.
Answer: Repair leaks and turn off taps while brushing.
Explanation: Both actions stop clean water from being wasted unnecessarily.