Why is "Assuming fresh water is abundant because most of Earth is covered by water." a common mistake in Water Sources and Supply?

Why it happens: Students know the Earth is ~71% water and assume it is all accessible. How to avoid it: Only ~2.5% of Earth's water is fresh; of that, ~70% is locked in ice and glaciers. Only about 0.3% of all water is accessible surface fresh water. Water scarcity is a genuine and growing global challenge.

Why is "Presenting desalination as a perfect solution to water scarcity." a common mistake in Water Sources and Supply?

Why it happens: Students know desalination produces fresh water from the sea, so they assume it solves the problem. How to avoid it: Desalination is expensive, uses huge amounts of energy (usually from fossil fuels), produces brine waste that harms marine ecosystems, and requires costly infrastructure — limiting its use to wealthy, water-scarce countries.

Why is "Confusing evaporation with condensation or using them interchangeably." a common mistake in Water Sources and Supply?

Why it happens: Students know both involve water and temperature but mix up direction. How to avoid it: Evaporation = liquid → gas (water warms and rises). Condensation = gas → liquid (water vapour cools and forms droplets/clouds). They are opposite processes. Evaporation removes water from surface; condensation returns it to clouds.

WaterCambridge IGCSE Environmental Management (0680)

Water Sources and Supply

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Water Sources and Supply — Cambridge IGCSE Environmental Management 0680

Fresh water is a finite and unevenly distributed resource. This subtopic covers the global water cycle, sources of fresh water, increasing demand, water scarcity, and strategies to ensure sustainable supply.

What you’ll learn

Mapped to the Cambridge IGCSE 0680 syllabus (2027-2029).

3.1a — Describe the global water cycle and the processes involved.
3.1b — Identify and describe the main sources of fresh water.
3.1c — Explain the causes of water scarcity and unequal distribution.
3.1d — Evaluate strategies to ensure sustainable water supply.

The Hydrological (Water) Cycle

Water continuously cycles between the oceans, atmosphere, land and living organisms.

The hydrological cycle describes the continuous movement of water through the Earth system. It is driven by solar energy (for evaporation and plant transpiration) and gravity (for precipitation and runoff).

Key processes:

Process	Description
Evaporation	Water changes from liquid to vapour, mainly from ocean surfaces
Transpiration	Water vapour released by plants through stomata
Evapotranspiration	Combined evaporation + transpiration
Condensation	Water vapour cools and forms clouds (water droplets on dust particles)
Precipitation	Water falls as rain, snow, sleet, hail
Surface runoff	Water flows over land into rivers and lakes
Infiltration	Water soaks into soil
Percolation	Water moves through soil into groundwater (aquifers)
Groundwater flow	Slow movement of water through rock and soil toward sea
Interception	Vegetation catches precipitation before it reaches the ground

Water balance: In any given area: Precipitation = Evapotranspiration + Runoff + Change in storage.

Areas with P > ET = water surplus (humid climates, e.g. UK, tropical rainforests).
Areas with ET > P = water deficit (arid regions, e.g. Sahara, Middle East).

Solar energy lifts water as vapour by evaporation and transpiration; gravity returns it as precipitation, runoff and groundwater — the hydrological cycle.

How human activities affect the water cycle:

Deforestation: Reduces interception and transpiration → more runoff → flooding; aquifers not recharged as efficiently.
Urbanisation: Impermeable surfaces → surface runoff instead of infiltration → aquifers not recharged; flooding increases.
Irrigation: Removes water from rivers and aquifers → reduces flow; returned water may be saline.
Climate change: Alters precipitation patterns; melts glaciers (short-term increase in meltwater, long-term reduction).

Solar energy drives evaporation; gravity drives precipitation and runoff.
Key processes: evaporation → condensation → precipitation → runoff/infiltration.
Deforestation: less interception and transpiration → more flooding, less groundwater recharge.
Urbanisation: impermeable surfaces → runoff not infiltrating → flooding.

Sources of Fresh Water

Rivers, lakes, aquifers and glaciers are the main fresh water sources — each with advantages and limitations.

Rivers and lakes (surface water):

Most easily accessible and widely used.
Recharged relatively quickly by rainfall.
Vulnerable to pollution, evaporation, and seasonal variation (flooding in wet season, low flow in dry season).
Rivers supply most urban water systems via reservoirs.

Groundwater (aquifers):

Underground layers of permeable rock that store and transmit water.
Recharged slowly by percolation from rainfall (rate of recharge depends on rock type).
More reliable than rivers in dry seasons.
Extraction: boreholes or wells drilled down to the aquifer.
Over-extraction: depletes aquifer faster than it recharges → aquifer depletion (water table falls).
Contamination from fertilisers, pesticides, septic tanks, industrial chemicals is a serious risk.
Ogallala Aquifer (USA): one of the world's largest; being extracted far faster than it recharges.

Glaciers and snowmelt:

Mountain glaciers store large quantities of fresh water as ice.
Meltwater feeds major rivers during summer (e.g. Indus, Ganges, Yangtze, Colorado).
Climate change is accelerating glacier retreat → initially more meltwater, then far less as glaciers disappear.
Billions of people depend on glacier-fed rivers.

Desalination:

Removes salt from seawater or brackish water to produce fresh water.
Methods: reverse osmosis (most common), multi-stage flash distillation.
✅ Abundant resource (ocean water); not rainfall-dependent; used widely in Middle East.
❌ Very energy-intensive; expensive; produces hypersaline brine that must be disposed of (marine impact).

Rainwater harvesting:

Collecting rainwater from rooftops into storage tanks.
Common in areas with seasonal rainfall.
✅ Low cost; decentralised; reduces pressure on rivers and aquifers.
❌ Dependent on rainfall timing; storage capacity limits supply.

Rivers/lakes: easily accessible; seasonal variation; pollution vulnerable.
Aquifers: reliable but slow recharge; over-extraction lowers water table.
Glaciers: supply rivers but retreating due to climate change.
Desalination: uses ocean water; energy-intensive; expensive; produces brine.
Rainwater harvesting: cheap, decentralised; seasonal.

Water Scarcity and Unequal Distribution

Water is unevenly distributed globally — physical and economic scarcity both limit access.

Global distribution of water:

Rainfall is extremely uneven — Amazon basin, Southeast Asia, and tropical West Africa are very wet; the Middle East, northern Africa and central Asia are very dry.
Major fresh water resources (rivers, lakes) are not always located where the population is largest.

Two types of water scarcity:

Physical scarcity — Not enough water in the natural environment to meet demand. Occurs in arid and semi-arid regions (Middle East, North Africa, parts of India).
Economic scarcity — Water exists but there is insufficient infrastructure (dams, pipes, treatment plants) or investment to access it. Occurs in sub-Saharan Africa — water may be present but people cannot access safe supplies.

Causes of increasing water demand:

Population growth: More people need more water for drinking, sanitation, food production.
Agriculture: Irrigation accounts for ~70% of global freshwater withdrawals. Growing more food for a larger population requires more water.
Industry: Manufacturing processes, cooling power stations, mining all require large amounts of water.
Rising living standards: As countries develop, water use per person increases (more showers, washing machines, swimming pools, irrigated gardens).
Climate change: Alters where and when rain falls; increases evaporation; reduces snowpack and glacier storage.

Consequences of water scarcity:

Crop failure and food insecurity.
Competition for water between countries sharing rivers (e.g. Nile Basin: Ethiopia's Grand Ethiopian Renaissance Dam vs. Egypt).
Water-borne diseases where people drink contaminated water.
Children (often girls) spending hours collecting water instead of attending school.
Political instability — water wars are a future risk.

Statistics:

~2 billion people live in areas of high water stress.
2 billion people lack safely managed drinking water.
3.6 billion people live in areas of water scarcity for at least one month per year.

Physical scarcity: not enough water. Economic scarcity: infrastructure absent.
Agriculture: ~70% of global freshwater withdrawals.
~2 billion people in high water stress areas.
Population growth + climate change = rising demand, falling supply in many regions.
Children spend hours collecting water → school attendance falls.

Strategies for Sustainable Water Supply

A combination of demand management and supply augmentation can ensure long-term water security.

Supply-side strategies (increase the amount available):

Dam and reservoir construction:

Store water during wet season for use in dry season.
Regulate river flow; can supply irrigation, drinking water, hydroelectric power.
❌ Flood valleys; displace communities; alter ecosystems; expensive.

Desalination:

Reverse osmosis or distillation of seawater.
Used in water-scarce but energy-rich regions (Middle East, Israel, Singapore).
❌ Very energy and cost intensive; brine disposal.

Rainwater harvesting:

Rooftop collection systems → storage tanks.
Low cost; used in rural areas of Africa, South Asia.

Aquifer recharge:

Deliberately directing surface water into the ground to replenish aquifers.

Interbasin water transfer:

Moving water from water-surplus to water-deficit regions via canals or pipes.
Example: South-to-North Water Transfer Project (China) — diverts Yangtze River water northward.
❌ Expensive; ecological impact on donor catchment.

Demand-side strategies (use less):

Water pricing:

Charge more for water → incentivises conservation; subsidises inefficient use.

Efficient irrigation:

Drip irrigation: water delivered directly to roots — 40–60% more efficient than flood irrigation.
Reduces water loss through evaporation and runoff.

Leak detection and repair:

In many cities, 20–50% of water is lost through leaking pipes before reaching consumers.
Fixing leaks is often more cost-effective than building new supplies.

Water recycling and reuse:

Treated wastewater reused for irrigation, industrial cooling, toilet flushing.
'Greywater' (used wash water) recycled within households for garden use.

Education and awareness:

Campaigns to reduce domestic water waste (shorter showers, fixing dripping taps, efficient appliances).

Legal frameworks:

International water law — rules governing shared rivers and aquifers.
UN Watercourses Convention (1997): countries sharing rivers must not cause significant harm to others; must cooperate on management.

Supply: dams, desalination, rainwater harvesting, aquifer recharge, interbasin transfer.
Demand: drip irrigation, leak repair, water pricing, recycling, education.
Drip irrigation: 40–60% more efficient than flood irrigation.
Many cities lose 20–50% of supply through leaking pipes — fixing leaks is cost-effective.
Desalination: effective but energy-intensive and expensive.

Sources: Cambridge IGCSE Environmental Management 0680 syllabus 2027-2029, Section 3.1; UN Water — World Water Development Report 2024; 0680/12 May/Jun 2022 — Q10 (water sources and scarcity). Last reviewed 2026-05-15.

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Step-by-step worked examples — Water Sources and Supply

Step-by-step solutions to past-paper-style questions on water sources and supply, written exactly the way a tutor would explain them at the board.

1Describe the water (hydrological) cycle
Core• water cycle, processes
Question
Describe the main processes of the water cycle and explain how they link to freshwater availability.
Step-by-step solution
1. Step 1
  Evaporation — solar energy heats surface water in oceans, lakes and rivers, converting liquid water to water vapour which rises into the atmosphere. This is the main input of moisture to the atmosphere.
2. Step 2
  Transpiration — plants absorb water through roots and release it as vapour through stomata in leaves. Together with evaporation, this is called evapotranspiration — a major output of water from terrestrial ecosystems.
3. Step 3
  Condensation and cloud formation — as water vapour rises and cools, it condenses around dust particles to form clouds of tiny water droplets or ice crystals.
4. Step 4
  Precipitation — water falls from clouds as rain, snow, sleet or hail. Some infiltrates into soil and recharges aquifers (groundwater), some flows as surface runoff into rivers and lakes, and some is intercepted by vegetation.
Answer
Evaporation/transpiration → condensation → precipitation → infiltration (groundwater recharge) or surface runoff (rivers and lakes). The cycle continuously redistributes fresh water.
Examiner tip
Key process terms to use: evaporation, transpiration, evapotranspiration, condensation, precipitation, infiltration, surface runoff, groundwater recharge. Questions may ask you to name 4–6 processes.
2Main sources of fresh water
Core• Adapted from 0680/12 Oct/Nov 2023• water sources, supply
Question
Identify and describe FOUR main sources of fresh water used for human consumption and agriculture.
Step-by-step solution
1. Step 1
  Rivers and lakes (surface water) — the most accessible source for many communities. Rivers supply water directly or are dammed to create reservoirs. Water is treated before drinking. Susceptible to pollution and seasonal variation.
2. Step 2
  Groundwater / aquifers — rain infiltrates through permeable rock and accumulates underground in aquifers. Extracted via boreholes or wells. A major source in regions with little surface water (e.g. Saudi Arabia, Bangladesh). Risk of over-extraction causing aquifer depletion.
3. Step 3
  Reservoirs (impounded water) — dams built across rivers create artificial lakes that store large volumes of water. They provide reliable year-round supply by capturing wet-season rainfall and releasing it during dry periods.
4. Step 4
  Desalination — removing salt from seawater or brackish water to produce fresh water. Used in water-scarce regions (e.g. UAE, Kuwait, Israel). Very energy-intensive and expensive but important where no freshwater alternatives exist.
Answer
Rivers/lakes (surface water), groundwater/aquifers (permeable rock storage), reservoirs (impounded river water), desalination (salt removal from seawater). Groundwater is the largest store; desalination is most expensive.
Examiner tip
Desalination appears frequently in exam questions — know its benefit (provides water in arid regions) and its limitations (high energy cost, expensive to build and operate, produces brine waste that can harm coastal ecosystems).
3Factors affecting water demand and supply
Core• demand, supply, factors
Question
Explain how THREE factors cause water demand to increase and describe ONE strategy for each factor to manage the resulting water stress.
Step-by-step solution
1. Step 1
  Population growth — more people means more domestic water use (drinking, sanitation, cooking) and more food needs (which requires irrigation water). Management: water metering — charging households per unit consumed incentivises conservation and reduces waste.
2. Step 2
  Agricultural expansion and irrigation — as global food demand rises, more land is irrigated. Agriculture accounts for ~70% of global freshwater withdrawal. Management: drip irrigation — delivers water directly to plant roots, reducing evaporation losses by up to 50% compared to flood irrigation.
3. Step 3
  Industrialisation and economic development — industries (paper, textiles, food processing) consume large volumes of water for cooling, washing and processing. Management: water recycling in industry — treating and reusing process water reduces freshwater withdrawals significantly.
Answer
Population growth (water metering to incentivise conservation), agricultural expansion (drip irrigation to reduce evaporation losses), industrialisation (water recycling in production processes).
Examiner tip
Remember: water stress occurs when demand exceeds sustainable supply. Climate change is also a key factor — altered precipitation patterns, increased evaporation and glacial retreat reduce supply. It is worth including in extended answers.
4Evaluate the construction of a large dam as a water supply strategy
Extended• Adapted from 0680/22 May/Jun 2024• dams, reservoirs, evaluate, multipurpose
Question
A government proposes building a large dam across a major river to create a reservoir that will supply water to a growing city of 5 million people. (a) Explain THREE benefits of the dam beyond water supply. (b) Evaluate the environmental and social costs of the dam. (c) Suggest whether the dam should be approved, giving a justified recommendation.
Step-by-step solution
1. Step 1
  Three benefits beyond water supply: (1) Hydro-electric power (HEP): the dam can generate electricity from the kinetic energy of water flowing through turbines in the dam wall. A large dam can supply electricity to hundreds of thousands of homes, reducing dependence on fossil fuels. (2) Flood control: by storing excess water during the wet season, the reservoir regulates river flow downstream, reducing the frequency and severity of floods that previously destroyed crops and homes. (3) Irrigation: the stored water can be released to irrigate farmland during the dry season, extending the growing season and increasing agricultural yields in the surrounding region.
2. Step 2
  Environmental costs: (1) Ecosystem destruction: the valley upstream of the dam is permanently flooded, destroying terrestrial habitats, forests and farmland. Downstream, reduced sediment and water flow alters river ecosystems — many species that depend on seasonal floods (e.g. migratory fish) cannot complete their life cycles. (2) Disruption of sediment transport: the dam traps sediment that would normally be carried downstream and deposited on floodplains and deltas. Over decades, this causes coastal erosion (e.g. Nile Delta shrinkage after the Aswan Dam) and reduces the fertility of downstream floodplain farmland. (3) Methane emissions: decaying vegetation in the reservoir generates methane (a potent greenhouse gas), particularly in tropical dams.
3. Step 3
  Social costs: (1) Displacement: large dams typically displace tens of thousands of people — communities living in the flooded valley must be relocated. Resettlement is often poorly managed; displaced people lose livelihoods, cultural sites and social networks (e.g. Three Gorges Dam displaced 1.2 million people). (2) Loss of cultural and archaeological heritage: historical sites, temples and burial grounds may be permanently submerged. (3) Downstream livelihoods: downstream fishing communities lose access to migratory fish; farmers lose fertile floodplain sediments and may need expensive fertilisers to maintain yields.
4. Step 4
  Recommendation: A conditional approval is defensible IF: (1) a thorough Environmental Impact Assessment (EIA) is conducted; (2) an independent resettlement plan with genuine community consultation is implemented; (3) minimum environmental flow releases downstream are mandated to maintain river ecosystems; (4) alternative water supply strategies (e.g. water recycling, demand management) have been shown to be insufficient for the city's needs. The dam should not be approved if alternatives are available and sufficient — large dams should be a last resort due to their irreversible impacts.
Answer
Dam benefits (beyond water): HEP generation, flood control, irrigation extension. Environmental costs: habitat flooding, sediment trapping (coastal erosion), methane emissions. Social costs: displacement (Three Gorges = 1.2 million), cultural heritage loss, downstream livelihood harm. Recommendation: conditional approval with EIA, resettlement plan, and minimum environmental flows.
Examiner tip
Dam evaluation questions are common in 0680. The sediment trapping and downstream delta/floodplain impact is the most sophisticated environmental cost — it earns marks that 'habitat loss' alone does not. The Three Gorges Dam (China) is the most important named example. For recommendations, a conditional 'yes' with conditions is more sophisticated than a simple 'no'.
5Analyse water stress in a data-based country scenario
Extended• water stress, data interpretation, management strategies
Question
Country Z is in a semi-arid region. Data: annual rainfall = 250 mm, population = 20 million (growing at 2% per year), agriculture accounts for 80% of water use, groundwater table falling 2 m/year, water demand exceeds supply by 15%. (a) Using the data, explain why Country Z faces severe water stress. (b) Recommend TWO strategies to reduce water stress in Country Z, justifying each with reference to the data.
Step-by-step solution
1. Step 1
  Why Country Z faces severe water stress: (1) Rainfall of only 250 mm/year is very low (the global average is ~990 mm) — below the threshold for reliable rain-fed agriculture. Evaporation in semi-arid regions typically exceeds 2,000 mm/year, meaning nearly all rainfall is lost before it can be stored. (2) Agriculture uses 80% of all water — in a water-stressed nation, irrigated agriculture at this scale is unsustainable. (3) The groundwater table is falling 2 m/year, meaning extraction from aquifers far exceeds natural recharge (which in an arid region may be near zero). This 'aquifer mining' is inherently finite — when the aquifer is exhausted, the water source is gone. (4) Demand already exceeds supply by 15% — this gap will grow as the population increases by 2% annually, compounding the crisis.
2. Step 2
  Strategy 1 — Introduce precision irrigation in agriculture: Since agriculture accounts for 80% of water use, even a modest efficiency improvement generates large absolute savings. Replacing flood irrigation with drip irrigation (which uses 30–50% less water) could reduce total national water use by 24–40% — potentially eliminating the 15% supply deficit. The data shows that this is the highest-leverage intervention because it targets the largest use sector. Justified by data: 80% of use × 30–50% savings = 24–40% total national savings.
3. Step 3
  Strategy 2 — Implement groundwater recharge programmes and regulate extraction: The 2 m/year decline in the water table indicates uncontrolled over-extraction. The government should: (1) meter all groundwater extraction and introduce licensing to limit pumping; (2) invest in managed aquifer recharge — diverting any excess surface water during rare rainfall events into recharge wells. Justified by data: if extraction is not regulated, the aquifer will be fully depleted within decades, removing 80% of agricultural water supply — a catastrophic outcome. Stabilising the groundwater table is a prerequisite for long-term food and water security.
Answer
Water stress causes: 250 mm/year rainfall (far below average), agriculture = 80% of use, groundwater falling 2 m/yr (over-extraction), demand already 15% above supply, 2% annual population growth. Strategy 1: drip irrigation (targets 80% use sector, saves 30–50% = 24–40% total savings). Strategy 2: groundwater licensing + managed recharge (stabilises aquifer before it is exhausted).
Examiner tip
Data interpretation questions require you to use specific numbers in your answer. 'Agriculture uses a lot of water' is worth 0; '80% of water use is agricultural, so reducing irrigation efficiency has the highest total impact' earns marks. Always trace the data to the strategy — show the logical link, including any calculations.
6Explain virtual water and evaluate water-smart trade policies
Extended• virtual water, water footprint, trade, evaluate
Question
(a) Explain the concept of 'virtual water' and give a named example. (b) Evaluate the argument that water-scarce countries should import water-intensive goods rather than producing them domestically.
Step-by-step solution
1. Step 1
  Virtual water: 'Virtual water' (also called 'embedded water') refers to the water consumed during the production of a food or manufactured product. When a country imports a good, it effectively imports the water used to make it, without using its own water resources. For example: producing 1 kg of beef requires approximately 15,000 litres of water (for animal feed, drinking and processing). A water-scarce country that imports beef from water-rich countries 'saves' 15,000 litres per kilogram — compared to raising the cattle domestically. This concept was developed by Tony Allan (1993) and is an increasingly important element of water resource management strategy.
2. Step 2
  Arguments FOR water-scarce countries importing water-intensive goods: (1) Water conservation: by importing water-intensive crops (wheat, rice, cotton) and meat, water-scarce countries preserve domestic water resources for essential uses (drinking, sanitation). (2) Economic efficiency: countries with water scarcity often cannot grow water-intensive crops competitively — they can produce other goods more efficiently and trade for food. (3) Food security via trade: global markets provide food security even when domestic production is impossible. Countries like Saudi Arabia, which once grew wheat using rapidly depleting fossil aquifers, have stopped and now rely on imports — a more sustainable approach.
3. Step 3
  Arguments AGAINST (limitations of this strategy): (1) Trade dependency and vulnerability: if a country imports most of its food, geopolitical crises, trade disputes, or global crop failures can instantly threaten food security — the COVID-19 pandemic and Ukraine war demonstrated the fragility of global supply chains. (2) Economic costs and foreign exchange: poor, water-scarce countries may lack the foreign exchange to import sufficient food — trade-based food security is only viable for wealthy nations. (3) Rural employment: domestic agriculture provides livelihoods in LICs; abandoning it for imports can cause rural unemployment and social unrest. (4) Environmental costs in exporting countries: concentrating water-intensive production in water-rich countries may cause environmental damage there (e.g. intensive irrigation in the US Midwest drawing down the Ogallala aquifer).
4. Step 4
  Conclusion: The virtual water trade strategy is theoretically sound and applicable for wealthy water-scarce countries (Gulf states, Israel). For poorer water-scarce nations, it requires careful consideration of trade vulnerability, employment, and food sovereignty. The best approach is a combination: reduce domestic water use through efficiency (drip irrigation) while strategically importing the most water-intensive commodities (beef, cotton) that cannot be produced domestically without depleting aquifers.
Answer
Virtual water = water embedded in goods; importing beef saves 15,000 L/kg vs. domestic production. FOR importing: conserves scarce water, economic efficiency, food security via trade. AGAINST: trade dependency (Ukraine war example), cost for poor nations, rural unemployment, aquifer impacts in exporting nations. Conclusion: viable for wealthy water-scarce countries; riskier for LICs without complementary efficiency measures.
Examiner tip
Virtual water is an Extended-level concept that tests application of water resource principles to global trade. The 15,000 L/kg beef figure is a compelling and memorable statistic. For evaluation, contrast the strategy's validity for HICs (Gulf states) vs. LICs — this distinction earns top-band marks. Always conclude with a nuanced position rather than 'imports are good/bad'.

Key Definitions and Keywords — Water Sources and Supply

Definitions to memorise and the exact keywords mark schemes credit for water sources and supply answers — sharpened from recent examiner reports for the 2026 0680 sitting.

Water (hydrological) cycle
Examiner keyword
The continuous movement of water between the atmosphere, land surface, oceans and underground, driven by solar energy and gravity. Processes include evaporation, transpiration, condensation, precipitation and infiltration.
Aquifer
Examiner keyword
An underground layer of permeable rock, sediment or soil that holds and transmits groundwater. Aquifers are recharged by precipitation infiltrating through the surface.
Related: groundwater, permeability, water cycle
Desalination
Examiner keyword
The process of removing dissolved salts from seawater or brackish water to produce fresh water suitable for drinking and irrigation. Methods include reverse osmosis and distillation. Highly energy-intensive.
Related: water supply, energy consumption
Water stress
Examiner keyword
A condition in which water demand exceeds the available supply, or when the quality of available water is too poor for use. Countries are water-stressed when they withdraw >20% of their annual renewable water resources.
Related: water scarcity, water supply, water demand
Evapotranspiration
The combined loss of water from a land surface through evaporation from soil and open water, and transpiration from plants. It is a major pathway by which water returns to the atmosphere.
Related: water cycle, transpiration, evaporation
Surface runoff
Water that flows over the land surface into streams and rivers without infiltrating the soil. It is increased by impermeable surfaces (roads, rooftops), saturated soil, steep slopes and heavy rainfall.
Related: water cycle, flooding, soil erosion

Common Mistakes and Misconceptions — Water Sources and Supply

The traps other students keep falling into on water sources and supply questions — taken from recent Cambridge IGCSE 0680 examiner reports and mark schemes — and how to avoid them.

✕Assuming fresh water is abundant because most of Earth is covered by water.
Why it happens
Students know the Earth is ~71% water and assume it is all accessible.
How to avoid it
Only ~2.5% of Earth's water is fresh; of that, ~70% is locked in ice and glaciers. Only about 0.3% of all water is accessible surface fresh water. Water scarcity is a genuine and growing global challenge.
✕Presenting desalination as a perfect solution to water scarcity.
Why it happens
Students know desalination produces fresh water from the sea, so they assume it solves the problem.
How to avoid it
Desalination is expensive, uses huge amounts of energy (usually from fossil fuels), produces brine waste that harms marine ecosystems, and requires costly infrastructure — limiting its use to wealthy, water-scarce countries.
✕Confusing evaporation with condensation or using them interchangeably.
Why it happens
Students know both involve water and temperature but mix up direction.
How to avoid it
Evaporation = liquid → gas (water warms and rises). Condensation = gas → liquid (water vapour cools and forms droplets/clouds). They are opposite processes. Evaporation removes water from surface; condensation returns it to clouds.

Past paper style quiz

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Water Sources and Supply

Detailed Notes

What you’ll learn

1Describe the water (hydrological) cycle

2Main sources of fresh water

3Factors affecting water demand and supply

4Evaluate the construction of a large dam as a water supply strategy

5Analyse water stress in a data-based country scenario

6Explain virtual water and evaluate water-smart trade policies

Water (hydrological) cycle

Aquifer

Desalination

Water stress

Evapotranspiration

Surface runoff

✕Assuming fresh water is abundant because most of Earth is covered by water.

✕Presenting desalination as a perfect solution to water scarcity.

✕Confusing evaporation with condensation or using them interchangeably.

Past paper style quiz