Cambridge IGCSE Environmental Management: Water — Revision Notes

Condensed for the final weeks. For the full explanation, use the Water study guide.

3.1 Water sources and supply — stores vs transfers

Revise the water cycle as two linked lists, since questions can ask for either separately:

Stores	Transfers
Oceans (salt water)	Precipitation
Ice sheets/glaciers	Interception
Ground water	Surface run-off
Atmosphere	Infiltration, through-flow
Lakes and rivers	Ground water flow
—	Transpiration, evaporation, condensation

Fresh water sources: atmosphere, surface water, ground water, desalinated ocean water. Potable water = safe to drink. Treatment stages in order: screening → sedimentation → filtration → chlorination.

Desalination method	Process
Distillation	Boil-condense cycle
Reverse osmosis	Pressure forces water through a membrane

Multipurpose dam uses (8): flood control, hydro-electric power, irrigation, storage, transport, recreation, tourism, fish farming — each doubles as a benefit; be ready to pair each with a documented limitation (e.g. HEP vs disrupted river ecosystems/downstream communities) for “discuss” questions.

3.2 Water pollution — cause-and-effect pairs

Source	Linked impact
Domestic waste, sewage	Infectious disease (e.g. cholera)
Industrial processes	Toxic substance accumulation
Agricultural practices	Eutrophication
(Air pollution route)	Acid rain harming aquatic organisms

Bioaccumulation vs biomagnification — the classic mix-up:

• Bioaccumulation: toxin builds up within a single organism over time.
• Biomagnification: that concentration increases further up a food chain, prey to predator.

Eutrophication as a full causal chain (name all four links for “explain” marks): nutrient enrichment → algal bloom → light blocked → oxygen depleted as algae decompose → aquatic life harmed.

3.3 Water-related diseases — don’t mix the two mechanisms

	Malaria	Cholera
Transmission	Vector-borne (female Anopheles mosquito)	Waterborne
Control	Personal protection, vector control	Handwashing, sanitation, potable water, vaccination

For “benefits and limitations” questions, name a specific limitation — insecticide resistance limiting spraying, or vaccination access gaps — rather than a generic “it’s expensive.”

3.4 Marine aquaculture — five outcomes, not the shortest sub-topic

Reasons wild stocks are exploited: overfishing, overharvesting — affecting both target and bycatch species and wider food chains. Marine aquaculture = farming marine species (fish, crustaceans, seaweeds) in captivity — species-specific knowledge is explicitly not required for that definition, but the sub-topic doesn’t stop there: also learn the impacts of aquaculture itself (reduced exploitation of wild fisheries, increased food supply, risk of escape and disease, effects on local food webs, nutrient enrichment, energy usage, source of food for farmed species) and the nine-item management list (boat/net size limits, increased mesh size, sustainable methods e.g. pole and line, quotas, closed seasons, limited fishing days, protected areas, conservation laws, international agreements). With five outcomes against 3.2’s three and 3.3’s four, this is one of the larger sub-topics in the topic, not the shortest.

3.5 Oil pollution

Causes: off-shore/on-shore extraction, pipelines, shipping, tank cleaning at sea, refineries. Impacts (species knowledge not required): birds, marine mammals, fish, crustaceans, seaweeds, coral reefs, beaches. Prevention: MARPOL (International Convention for the Prevention of Pollution from Ships), double-hulled tankers, risk assessments, regular maintenance. Minimising spill impact: improved navigation, booms and sorbents, detergent sprays, skimmers, controlled burning. Keep prevention and impact-minimising as two separate lists — a question can ask for either alone.

3.6 Plastic pollution — new for this cycle

Conventional plastics: fossil-fuel-derived, generally non-biodegradable. Bioplastics: made fully/partly from biological material, can themselves be biodegradable or not — don’t assume “bio-” means it breaks down. Microplastics: less than 5mm, formed when larger plastics break down. Impacts on marine ecosystems: visual pollution, entanglement, being mistaken for food, bioaccumulation and biomagnification. Management: alternative packaging, avoiding single-use plastics, safe disposal, recycling, legislation and enforcement.

Worked example: desalination trade-off

A coastal country with limited fresh water is deciding between distillation and reverse osmosis for a new desalination plant.

Distillation:     Boils seawater, then condenses the vapour --
                   energy-intensive (heating requires significant
                   fuel/electricity), but a well-established, reliable
                   technology.
Reverse osmosis:  Forces water through a membrane under pressure --
                   generally lower energy use than distillation, but
                   membranes require regular maintenance/replacement
                   and are vulnerable to fouling from particles in
                   the seawater.
Trade-off:        Both methods buy water security independent of
                   rainfall, but at a real ongoing energy and
                   maintenance cost -- exactly the "benefit vs
                   limitation" structure examiners reward, rather
                   than presenting desalination as a cost-free fix.

Practising this exact trade-off framing — a genuine water-security benefit weighed against a genuine energy/maintenance cost — transfers directly to “discuss the benefits and limitations” questions on multipurpose dams too, since both sub-topics reward the same evaluative structure.

Command words for this topic

“Water” questions in Paper 1 mix short recall with longer evaluative items. Match your answer’s length to the command word rather than writing the same amount for every question:

Command word	What’s expected
State / Identify	A single named fact — a store, a transfer, a disease
Describe	The pattern or process, in sequence, without explaining causes
Explain	The cause-and-effect chain — e.g. the four-step eutrophication sequence
Discuss	Benefits and limitations, reaching a judgement where asked

A “discuss the benefits and limitations of multipurpose dams” question that only lists benefits, however accurately, cannot access the full mark range — the limitations half is not optional extra detail, it is a separate assessment objective.

Worked example: treatment stage recall

A question gives a diagram of a water treatment works with one stage unlabelled and asks you to identify it and state its purpose.

Sequence:   screening -> sedimentation -> filtration -> chlorination
If stage 3 (filtration) is blanked out:
Identify:   Filtration
Purpose:    Removes the smaller suspended particles that did not
            settle out during sedimentation and were too small for
            screening to catch, using sand/gravel beds the water passes
            through, before the water is disinfected at the final
            chlorination stage.

Learning the four-stage sequence in strict order, rather than as an unordered list, is what makes “which stage comes before/after X” questions and diagram-labelling questions straightforward rather than a guessing exercise.

Exam traps

• Confusing bioaccumulation (within one organism) with biomagnification (increasing up a food chain).
• Listing multipurpose dam uses without a paired limitation when “discuss” is the command word.
• Applying malaria’s vector-control strategies to a cholera question, or vice versa.
• Adding named-species detail to the marine-aquaculture definition outcome specifically (the rest of 3.4 is not species-restricted).
• Naming eutrophication without tracing the full causal chain from nutrient enrichment to harmed aquatic life.
• Stopping revision at marine aquaculture and forgetting oil pollution (3.5) and plastic pollution (3.6), the topic’s last two sub-topics.
• Assuming a bioplastic automatically biodegrades.

Self-test

1. Name three “transfers” and three “stores” in the water cycle.
2. What’s the difference between bioaccumulation and biomagnification?
3. Trace the eutrophication causal chain in four steps.
4. How do malaria and cholera differ in transmission and control?
5. Name the international convention on preventing ship pollution, and one strategy for minimising an oil spill’s impact once it has happened.
6. Give the numerical threshold that defines a microplastic.

Answers: 1. Transfers: precipitation, infiltration, evaporation (or any three named); stores: oceans, ice sheets/glaciers, ground water (or any three named). 2. Bioaccumulation is a toxin building up within a single organism over time; biomagnification is that concentration increasing further as it moves up a food chain from prey to predator. 3. Nutrient enrichment → algal bloom → light blocked → oxygen depleted as algae decompose, harming aquatic life. 4. Malaria is vector-borne (mosquito to human) and controlled via personal protection and vector control; cholera is waterborne and controlled via sanitation, safe water and vaccination. 5. MARPOL (the International Convention for the Prevention of Pollution from Ships); any one of improved navigation systems, booms and sorbents, detergent sprays, skimmers, or controlled burning. 6. Less than 5mm in length.