IB ESS HLTopic 4 — Water Access, Use & SecurityPaper 1 & 2HL only~10 min read
What Causes Water Stress
Water stress is a tougher test than water scarcity. Scarcity asks one question: is there enough? Stress asks four, and a region can pass the first and still fail badly on the rest.
📘 What you need to know
Water stress considers quantity, quality, environmental flows and accessibility.
Water scarcity considers only the absolute shortage of water.
A region is water stressed when clean, accessible supply falls below 1700 m3 per person per year.
Environmental flows are the water rivers, lakes and wetlands need to stay healthy — not water that is spare for us.
Major causes: industrialisation in emerging economies and population pressure with over-abstraction in lower-income countries.
Shared rivers create transboundary disputes, as with the Nile.
Stress is scarcity plus three more tests
This is the single most examinable idea on the page. If you can explain why stress is a broader measure than scarcity, most questions here become straightforward.
Environmental flows
Rivers, lakes and wetlands need a certain amount of water to stay healthy — enough to keep fish populations going, move sediment, and support the species that live there. That share is called the environmental flow.
When too much is abstracted for irrigation or industry, the flow drops below what the ecosystem needs. Habitats degrade, biodiversity falls, and the river’s ability to dilute pollution weakens, which makes the water quality problem worse too.
Accessibility
Water can exist and still be out of reach. Accessibility depends on:
Infrastructure — pipes, pumps, wells and treatment works.
Distance — how far people have to travel to a source.
Affordability — whether households can pay the price charged.
The 1700 threshold
Water stress has a working definition you should learn: available clean, accessible supply of less than 1700 m3 per person per year. That figure covers everything a person indirectly needs — not just drinking and washing, but the water used by the agriculture and industry that supports them.
Learn the 1700 figure and the two bands below it. Questions often give you a total supply and a population and expect you to place the country on this scale.
What causes water stress
Industrialisation in emerging economies
Rapid industrial growth needs water for factories, cooling and energy production, on top of rising urban demand.
Northern China is the standard example: heavy industrial growth in a region with limited fresh water to start with.
The result is competition between industry, farming and households for the same rivers and aquifers.
Industry also degrades quality, so water used once may not be usable again — a stress problem as much as a scarcity one.
Population pressure and over-abstraction
Growing populations push demand up faster than storage and distribution can be built.
Where infrastructure is limited, farmers turn to groundwater, pumping faster than aquifers recharge.
Northern India is the widely cited case, where rural irrigation depends heavily on groundwater and water tables have fallen.
Over-abstraction lowers the water table, so wells must go deeper, costs rise, and poorer farmers are pushed out first.
When rivers cross borders
Roughly every large river basin is shared, and shared water invites disagreement. The Nile flows through eleven countries, and tensions between Egypt and Ethiopia have grown around the Grand Ethiopian Renaissance Dam.
The logic is the same in every transboundary dispute:
The upstream country can store or divert water, and gains power and irrigation from doing so.
The downstream country depends on flow it does not control — Egypt relies on the Nile for most of its farming and drinking water.
Filling a large reservoir reduces downstream flow temporarily, which is when disputes usually sharpen.
History, politics and environmental change make agreement harder, so treaties and joint management bodies become essential.
If you can explain the upstream and downstream logic, you can analyse any shared basin in the exam — the Nile, the Mekong, the Indus or one you have never heard of.
What water stress does
Agriculture. Too little irrigation water means lower yields and food insecurity.
Economy. Water-hungry industries such as energy, textiles and food processing slow or stop, costing jobs and output.
Health. Where supply is short and quality poor, waterborne diseases such as cholera and dysentery spread.
Ecosystems. Environmental flows fall, habitats degrade and freshwater biodiversity declines.
Worked examples
WORKED EXAMPLE 1
Is this country water stressed?
A country has 34 billion m3 of clean, accessible water per year and a population of 25 million. Calculate the supply per person and classify it.
Step 1: divide supply by population34 000 000 000 ÷ 25 000 000 = 1360 m3 per person per yearStep 2: compare with the thresholds
Below 1700 but above 1000
Water stressed, but not yet water scarceadd a sentence for the top mark: if the population grows to 34 million, supply per head falls to 1000 m3 and the country becomes water scarce
WORKED EXAMPLE 2
Distinguish water stress from water scarcity [3]
A region receives high rainfall, yet 40% of its people cannot get safe water. Explain which term applies.
Point 1Scarcity is about quantity alone, and high rainfall means quantity is not the problem
Point 2Stress also counts quality, environmental flows and accessibility
Point 3
Here water is present but polluted or unreachable, so people still go without
The region is water stressed, not water scarceexam questions love this setup: plenty of rain, still no safe water
WORKED EXAMPLE 3
Explain how industrialisation causes water stress [4]
Use a named region.
Link 1
Rapid industrial growth in northern China raises demand for cooling and processing water
Link 2
Urban populations grow alongside the factories, so domestic demand rises too
Link 3
Industry, farming and households now compete for limited local supplies
Link 4
Industrial discharge degrades water quality, shrinking usable supply further
Demand rises, usable supply falls, so stress increasesthe fourth link is the one that turns a scarcity answer into a stress answer
💡 Exam tip
Open any stress answer by naming the four components: quantity, quality, environmental flows, accessibility.
Learn 1700 m3 per person per year as a number you can quote and calculate with.
Use named regions: northern China for industrialisation, northern India for over-abstraction, the Nile for disputes.
Explain environmental flows as water that belongs to the ecosystem, not water going spare.
For transboundary questions, structure around upstream control and downstream dependence.
Cover impacts across agriculture, economy, health and ecosystems — four categories, easy marks.
⚠ Common mix-up
Using stress and scarcity interchangeably. Stress is the broader measure.
Forgetting quality. Polluted water counts as unavailable.
Thinking the 1700 figure is only drinking water. It includes agriculture and industry too.
Treating environmental flows as a luxury. Below them, ecosystems fail and water quality declines further.
Assuming a shared river always means conflict. The Indus Waters Treaty shows cooperation is possible.
Blaming population growth alone. Consumption per person and industrial demand often matter more.
Up next: Responding to Water Stress — the large-scale engineering options, from dams and pipelines to cloud seeding and desalination, and the environmental price tag on each.
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