Cambridge O Level Environmental Management (5014): Water – Study Guide

Water is needed for drinking, farming, industry and sanitation, yet only a small share of the world’s water is fresh and easy to reach. This topic covers where people get water, how it becomes polluted, the diseases linked to unsafe water, and the environmental effects of fish farming, oil and plastic in the sea. For each section, aim to be able to state a cause, an impact on people or ecosystems, and a way of managing the problem.

Where this fits in the course

In Cambridge O Level Environmental Management (5014) for 2027 to 2029, Topic 3 has six sub-topics: water sources and supply, water pollution, water-related diseases, marine aquaculture, oil pollution and plastic pollution. It follows the topics on the environment and land, and it connects strongly to Topic 4, because climate change alters rainfall and therefore supply.

Water sources and supply

Fresh water comes from surface water (rivers, lakes and reservoirs), groundwater held in aquifers and reached by wells and boreholes, and rainwater collected from roofs. Where fresh water is scarce, some coastal countries use desalination to remove salt from sea water.

Source	Advantage	Disadvantage
Reservoir	Stores large amounts for dry seasons	Floods land, displaces people, loses water to evaporation
Groundwater	Often clean and available all year	Over-extraction lowers the water table; slow to refill
Rainwater harvesting	Cheap and simple at household scale	Depends on rainfall; storage tanks needed
Desalination	Reliable supply from the sea	High energy cost; salty waste water

Demand for water rises with population, irrigation and industry. Water can be used more sustainably by repairing leaks, using drip irrigation, recycling waste water, charging for use and educating households.

Water pollution

Common pollutants and their sources:

• Sewage from homes and towns, containing organic matter and microorganisms.
• Fertilisers and animal waste washed off farmland, containing nitrates and phosphates.
• Industrial waste, which can contain heavy metals and chemicals.
• Pesticides washed from fields.
• Heated water from cooling in factories and power stations.

Eutrophication

When fertiliser or sewage enters a lake, the extra nutrients cause rapid growth of algae. The algae form a thick layer that blocks light, so plants below die. Bacteria then decompose the dead material and use up the dissolved oxygen. Fish and other animals die of oxygen shortage. Make sure you give the stages in order, since marks are usually awarded for the chain of reasoning.

Management

Treat sewage before release, limit and time the use of fertilisers, create buffer strips of vegetation along rivers, regulate industrial discharge and monitor water quality. Indicator species and oxygen measurements are used to judge how polluted a river is.

Water-related diseases

Several diseases are linked to water in different ways.

• Water-borne diseases are spread by drinking or using contaminated water, for example cholera and typhoid, which are caused by microorganisms from human waste.
• Water-based and water-related insect diseases depend on animals living in or near water; malaria is spread by mosquitoes that breed in standing water.

Prevention depends on safe drinking water, sanitation and hygiene: treat or boil water, build latrines away from wells, cover or drain stagnant water, use bed nets, wash hands, and provide rehydration treatment for diarrhoeal disease. Poor communities with no piped supply carry the greatest burden, and women and children often spend many hours collecting water.

Marine aquaculture

Marine aquaculture is the farming of fish, shellfish and seaweed in the sea, often in floating net cages. It provides protein, reduces pressure on wild fish stocks and creates jobs.

Environmental problems include waste food and faeces that enrich the water below cages, the spread of disease and parasites to wild fish, escaped fish breeding with wild populations, antibiotic and chemical use, and clearance of mangroves for ponds. Better practice includes siting farms where currents disperse waste, controlling stocking density, using properly designed feed and rotating sites.

Oil pollution

Oil enters the sea through tanker accidents, offshore drilling leaks, pipeline faults and illegal cleaning of tanks. A thick layer floats and spreads on the surface.

Impacts

• Seabirds lose the waterproofing of their feathers and may die of cold or by swallowing oil.
• Marine mammals and fish are poisoned; shellfish accumulate toxins.
• Oil smothers shores, mangroves and coral reefs.
• Tourism and fishing suffer, and clean-up is expensive.

Responses

Booms contain the slick, skimmers collect oil from the surface, dispersants break it into small droplets, absorbent materials mop up oil on beaches, and people clean wildlife. Each method has limits: dispersants may harm marine life and rough seas make booms ineffective. The best strategy is prevention, using double-hulled tankers, strict regulation, navigation controls and regular maintenance.

Plastic pollution

Plastic is cheap and durable, which is why it persists. It reaches the sea from rivers, litter, fishing gear and poor waste management. Large pieces entangle animals or are eaten by them, and sunlight and waves break plastic into microplastics that enter food chains. Floating plastic gathers in ocean gyres and drifts on to beaches.

Management includes reducing single-use plastic, reuse and recycling, better waste collection, deposit schemes, cleaning rivers and beaches, bans on certain items and education. Because plastic crosses borders, international cooperation is useful, though enforcement is difficult.

Worked example 1: household water use

A village has 850 people. Each person uses an average of 40 litres per day.

1. Daily use = 850 x 40 = 34,000 litres.
2. In cubic metres: 1 m cubed = 1,000 litres, so 34,000 / 1,000 = 34 cubic metres per day.
3. Per year = 34 x 365 = 12,410 cubic metres.

If a new tap system raises use to 55 litres per person, daily use becomes 850 x 55 = 46,750 litres, an increase of 12,750 litres, or 37.5 per cent.

Worked example 2: rainwater harvesting

A school roof has an area of 120 square metres. The annual rainfall is 650 mm. Assume that 80 per cent of the rain falling on the roof is collected.

1. 650 mm = 0.65 m, so rain falling = 120 x 0.65 = 78 cubic metres.
2. Collected = 78 x 0.80 = 62.4 cubic metres = 62,400 litres per year.
3. Per day on average = 62,400 / 365 = 171 litres (to the nearest litre).

Common mistakes

• Describing eutrophication as the death of fish from poison, instead of oxygen loss after algal growth.
• Mixing water-borne diseases with mosquito-borne diseases.
• Listing “clean up the oil” without naming a method.
• Treating plastic as only a litter problem and missing the effect of microplastics.
• Forgetting to convert litres and cubic metres.

Exam technique

Command words: state needs a short fact, describe a feature, explain a reason, suggest an application to an unfamiliar case, and discuss both sides. For sequence questions, number your steps. For management questions, say how the method works and one drawback. In context questions, use the place, scale and people described in the stimulus rather than giving a general list.

Check your understanding

1. Name three sources of fresh water for human use. (For example river, groundwater and rainwater.)
2. Give one drawback of groundwater over-extraction. (Lowers the water table and may dry wells.)
3. Put in order: algae die, oxygen falls, nutrients enter, algae bloom. (Nutrients enter, algae bloom, algae die, oxygen falls as bacteria decompose them.)
4. Give one water-borne disease and one way to prevent it. (Cholera; treating or boiling drinking water.)
5. State one environmental problem of marine fish farms. (Waste enriches water, disease spreads to wild fish, or escapes.)
6. Give one method of cleaning up an oil spill and a limitation. (Booms; ineffective in rough seas.)
7. What are microplastics? (Very small fragments formed when plastics break down, which enter food chains.)
8. A town of 2,000 people uses 30 litres each per day. How many cubic metres a day? (60,000 litres = 60 cubic metres.)

Frequently asked questions

What is eutrophication? When fertiliser or sewage enters a lake, the extra nutrients cause rapid growth of algae. When the algae die, decomposing bacteria use up the oxygen in the water, so fish and other animals die.

What is the difference between water-borne and mosquito-borne diseases? Water-borne diseases, such as cholera and typhoid, are spread by drinking or using contaminated water. Water-related insect diseases such as malaria depend on animals living in or near water, here mosquitoes that breed in standing water. Mixing the two up is a common mistake.

How are oil spills cleaned up? Booms contain the slick, skimmers collect oil from the surface and dispersants break it into small droplets. Naming a specific method earns more than “clean up the oil”.

How do you convert litres to cubic metres? Divide by 1,000, because 1 cubic metre is 1,000 litres. Forgetting to convert between litres and cubic metres is a common error in water-use calculations.

What are microplastics? Microplastics are very small fragments formed when plastics break down, and they enter food chains. This is why plastic is more than a litter problem.