Cambridge IGCSE Environmental Management 3: Water

Cambridge IGCSE Environmental Management 0680 Topic 3 covers water stores and supply, pollution, water-related disease, marine aquaculture and harvesting, oil pollution and plastic pollution. These notes follow official sections 3.1 to 3.6 for 2027 to 2029; field measurements remain in the separate fieldwork hub.

1. Water cycle, sources and potable supply

Water stores include oceans, ice sheets and glaciers, groundwater, the atmosphere, lakes and rivers. Transfers include precipitation, interception, surface runoff, infiltration, through-flow, groundwater flow, transpiration, evaporation and condensation. A store is where water remains; a transfer moves it.

People obtain fresh water from rain and snow, rivers, lakes and reservoirs, aquifers and wells, and desalinated ocean water. The five oceans are Pacific, Atlantic, Indian, Southern and Arctic. Potable water is safe to drink, not necessarily chemically pure.

Conventional treatment uses screening to remove large debris, sedimentation to settle suspended material, filtration to remove smaller particles and chlorination to kill many pathogens. Each stage has a different function.

Availability differs between water-rich and water-poor regions and between urban and rural communities. Physical supply, infrastructure, treatment, income, governance and sewage systems all affect access. National abundance does not ensure household access.

2. Desalination and dams

In distillation, salty water boils, salts remain, and steam is condensed as fresh water. Reverse osmosis applies high pressure to force water through a membrane that stops most ions and other molecules. Both can provide reliable coastal supply but require energy, capital, maintenance and management of concentrated brine.

Multipurpose dams can control floods, generate hydroelectricity, store irrigation and drinking water, support transport, recreation, tourism and fish farming. Limitations include high cost, displacement, flooded habitats, trapped sediment, altered downstream flow and fish movement, evaporation and the risk that benefits are distributed unequally.

3. Water pollution

Sources include domestic waste, sewage, plastic, industrial processes and agriculture. Untreated sewage can transmit cholera. Industrial toxins may accumulate in one organism over time, called bioaccumulation, and rise in concentration at higher food-chain levels, called biomagnification.

Acid rain can lower lake and river pH, harming organisms. Fertiliser ions and organic waste can enrich water. Algal growth blocks light; decomposers consume oxygen as biomass dies; oxygen depletion kills aquatic organisms. This eutrophication chain should be explained, not merely named.

Water quality improves through sanitation, sewage treatment, pollution controls, legislation and enforcement. Laws without monitoring, treatment capacity and penalties have limited effect.

4. Malaria and cholera

Female Anopheles mosquitoes transmit the Plasmodium malaria parasite when biting humans. An uninfected mosquito can acquire parasites by feeding on an infected person and later transmit them.

Personal protection includes bed nets, repellent, vaccination and antimalarial drugs. Vector control includes covering or draining breeding water, area insecticide spraying, sterilising males and biological control. Benefits must be weighed against cost, access, resistance, non-target impacts and continuing maintenance.

Cholera spreads through water or food contaminated by infected faecal material. Control includes handwashing, sanitation and sewage treatment, potable supplies through boiling or chlorination, and vaccination. Treatment of cases is important clinically, but the syllabus management list focuses on interrupting transmission.

5. Marine harvesting and aquaculture

Overfishing and overharvesting reduce target populations, kill bycatch and alter food chains. Marine aquaculture farms fish, crustaceans or seaweeds in captivity. It can increase food supply and reduce pressure on some wild fisheries, but escaped organisms, disease, waste nutrients, energy use and feed sourced from wild species can shift rather than remove impacts.

Harvest management includes limits on boat or net size, larger mesh, pole-and-line methods, quotas, closed seasons, limited fishing days, protected areas, conservation laws and international agreements. Effective rules need implementation and monitoring. A larger mesh allows smaller individuals to escape, while a closed season can protect breeding periods.

6. Oil pollution

Oil enters marine and coastal systems through offshore and onshore extraction, pipelines, shipping, tank cleaning and refineries. It coats bird feathers and mammal fur, reducing insulation and buoyancy, damages fish and crustaceans, blocks light and gas exchange for seaweeds and corals, and contaminates beaches.

Prevention includes MARPOL rules, double-hulled tankers, risk assessment and maintenance. Improved navigation reduces collision risk. After a spill, booms contain oil, sorbents absorb it and skimmers remove it. Detergents disperse oil but may increase exposure in the water column; controlled burning removes surface oil but creates air pollution. Response choice depends on oil type, weather, location and sensitive habitats.

7. Plastic pollution

Conventional plastics are generally non-biodegradable and made from fossil fuels. Bioplastics are fully or partly made from biological raw materials and may be biodegradable or non-biodegradable. Biodegradable plastics are designed for microbial decomposition in water or soil into water, biomass and gases, but rates depend on biotic and abiotic conditions.

Non-biodegradable plastics break down over long periods rather than disappearing. Microplastics are under 5 mm, formed by breakdown or used in products. Plastic causes visual pollution, entanglement and ingestion and can contribute to bioaccumulation and biomagnification of associated contaminants.

Management includes alternative packaging, avoiding single-use items, safe disposal, recycling, legislation and enforcement. Alternatives must be evaluated for actual disposal conditions, material use and lifecycle impact.

Worked example: managing a polluted coastal catchment

A coastal town has untreated sewage, fertiliser runoff, declining fish catches and plastic near aquaculture cages. A defensible plan separates pathways. Sewage treatment and chlorinated potable supply reduce cholera risk; riparian vegetation and controlled fertiliser application reduce nutrient entry; larger mesh, a breeding-season closure and monitored quotas protect wild stocks; cage density and feed controls limit aquaculture waste; deposit-return and enforced collection reduce plastic leakage. Monitoring should track faecal indicators, nutrients, dissolved oxygen, catch size and litter. One visible beach clean-up is insufficient because it removes symptoms but not sewage, runoff or fishing pressure. Costs, enforcement capacity and effects on fishers must shape the staged implementation.

Common misconceptions and how to correct them

• Calling evaporation a water store. It is a transfer.
• Defining potable as pure water. It means safe to drink.
• Saying filtration disinfects all water. Chlorination targets pathogens.
• Assuming global water abundance means equal access. Infrastructure and income matter.
• Saying reverse osmosis boils water. It uses pressure and a membrane.
• Calling dams entirely renewable and harmless. Reservoirs transform ecosystems and communities.
• Confusing bioaccumulation with biomagnification. One occurs within an organism; the other across trophic levels.
• Skipping oxygen depletion in eutrophication. Decomposition raises oxygen demand.
• Calling mosquitoes the malaria pathogen. They are vectors for Plasmodium.
• Assuming insecticide control has no trade-off. Resistance and non-target effects can occur.
• Calling aquaculture automatically sustainable. Feed, disease, escape and waste matter.
• Assuming quotas enforce themselves. Monitoring and agreements are essential.
• Using dispersants as if they remove oil. They redistribute it into droplets.
• Calling every bioplastic biodegradable. Feedstock and degradability are separate properties.
• Saying biodegradable plastic decomposes rapidly everywhere. Conditions control its rate.
• Assuming recycling alone prevents marine plastic. Avoidance, collection and enforcement also matter.

Assessment guidance

Use the named stores, transfers, treatment stages, pollutants, disease controls and management strategies in the syllabus. Explain mechanisms as linked sequences, especially eutrophication, disease transmission and food-chain contamination. For “discuss”, balance water or food benefits against energy, ecological, financial and social limitations before making a conditional judgement. Distinguish prevention from response for oil and plastic pollution. Comparisons should identify the context that changes effectiveness, such as coast, income, infrastructure, enforcement or habitat sensitivity. Keep sampling equipment and measurement protocols in the separate fieldwork notes.

Retrieval practice

Draw and label the water cycle, then compare four supply sources and both desalination methods. Sequence potable-water treatment and eutrophication. Contrast malaria and cholera transmission and control. Evaluate a dam, aquaculture project and fisheries plan. Match oil prevention and response tools to scenarios, classify conventional, bio-, biodegradable and microplastics, and design a catchment plan addressing sources rather than symptoms.

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