The water cycle, fresh-water sources and treatment
Trace water through stores and transfers, identify sources used by people and explain how treatment makes water potable.
Section 3 · Water
This original StudyForA sequence supports Cambridge IGCSE Environmental Management 0680 Topics 1–4 for exams in 2027, 2028 and 2029. Named local examples are chosen by the learner and centre; verify current conditions and local context with reliable sources. It is not a Cambridge paper, official grade or complete course.
Before you begin
- Use the 2027–2029 syllabus and check your exam year and centre's entry arrangements. Topics 1–4 are taught on this page; Topics 5–7 are still being built.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which sequence matches the syllabus treatment stages?
What you will learn
- Trace water through stores and transfers, identify sources used by people and explain how treatment makes water potable.
- Use evidence from an unfamiliar case to explain a cause-and-effect link and justify a suitable response.
Read the water cycle as stores and transfers
The syllabus stores include salt water in oceans and fresh water in ice sheets and glaciers, groundwater, the atmosphere, lakes and rivers. Water transfers include precipitation, interception, surface runoff, infiltration, through-flow, groundwater flow, transpiration, evaporation and condensation.
A cycle diagram shows linked movements, not a one-way path. For example, precipitation may be intercepted by vegetation, flow over the surface or infiltrate into soil; groundwater can later flow toward a river or sea.
Identify human fresh-water sources
People obtain fresh water from rain and snow in the atmosphere, rivers, lakes and reservoirs at the surface, and aquifers and wells underground. Desalination plants process ocean water; they require energy and infrastructure.
The five oceans named in the syllabus are Pacific, Atlantic, Indian, Southern and Arctic. Potable water is water that is safe to drink; clear appearance alone does not prove potability.
Explain the treatment sequence
The specified stages are screening, sedimentation, filtration and chlorination. Screening removes larger material; sedimentation allows suspended particles to settle; filtration removes further particles; chlorination disinfects water by controlling harmful microorganisms.
Treatment is a sequence. It does not mean that every water source begins with the same contamination, and safe supply also depends on storage and distribution that avoid later contamination.
Sources for this lesson
Pause and explain
Which is a groundwater source used by people?
Worked example
Water falls as rain, runs across a field, enters a river and is taken to a treatment plant. Identify two transfers and put the four treatment stages in order.
Show the worked solution
- Rain is precipitation; movement across the land is surface runoff.
- Water is first screened, then allowed to settle during sedimentation.
- It is filtered and then chlorinated before distribution, with safety checks as required.
Answer Precipitation and surface runoff describe transfers. Treatment follows screening, sedimentation, filtration and chlorination. The source and distribution system still need monitoring.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
After rainfall, some water is caught on leaves, some flows across a slope and some enters the soil. Name each process and explain one possible route to a river.
Give me a hint
Match each observation to interception, surface runoff or infiltration.
Compare my reasoning
- Water caught on leaves is interception.
- Water flowing across the slope is surface runoff; water entering the soil is infiltration.
- Runoff may reach a river directly, while infiltrated water can move as through-flow or groundwater flow.
The processes are interception, surface runoff and infiltration. Water may reach a river by surface runoff, through-flow or groundwater flow depending on the location.
Look for these in your work
- Three observations matched
- At least one route to a river explained
- Different transfers kept distinct
A settlement uses river water for drinking. Explain the treatment stages in order and give one reason that the word 'potable' is stronger than 'clear'.
Give me a hint
Separate physical removal from disinfection and safety.
Compare my reasoning
- Screening removes larger objects, and sedimentation lets suspended particles settle.
- Filtration removes additional particles, then chlorination disinfects the water.
- Potable means safe to drink; clear appearance does not show whether harmful microorganisms or chemicals remain.
The sequence is screening, sedimentation, filtration and chlorination. Potable means safe to drink, while clarity alone is only an observation and cannot establish safety.
Look for these in your work
- Order correct
- Purpose of final treatment included
- Safety meaning distinguished from appearance
A water-cycle diagram shows snow on a mountain, melting ice, a river, evaporation and cloud formation. Describe a valid sequence that returns water to the mountain and name the stores and transfers.
Give me a hint
Use stores as locations and transfers as movements or changes between them.
Compare my reasoning
- Snow and glacier ice are fresh-water stores; meltwater can enter a river and flow toward a lake or sea.
- Evaporation transfers liquid water to the atmosphere, where condensation forms clouds.
- Precipitation returns water to higher land; the diagram should show a cycle with multiple possible paths.
Water can move from glacier storage into a river, evaporate into the atmosphere, condense into clouds and return as precipitation. The stores and transfers form a cycle rather than a single fixed route.
Look for these in your work
- Stores and transfers distinguished
- Evaporation and condensation used correctly
- Cycle completed
Common mistakes
- Calling every water store fresh water
- Confusing infiltration with surface runoff
- Assuming clear water is potable
- Changing the order of the treatment stages
What can you explain now?
What does potable mean?
Compare with the explanation
Safe to drink
The correct answer is “Safe to drink”. The alternatives “Collected from an ocean” and “Visible without colour” do not match the syllabus concept. Trace water through stores and transfers, identify sources used by people and explain how treatment makes water potable.
After trying it yourself, choose your next review. This is your self-assessment.
Your review choice appears on Today. Sign in to sync it across devices.
Make it stick
Name the main freshwater sources, define potable water and recount the treatment sequence.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.