Key Idea: Most marks in topic 4.2 come from increasing supplies and water scarcity. At HL, also learn water stress, transboundary disputes and the freshwater planetary boundary.
1. Increasing supplies (most marks)
- Dams and reservoirs store water, but flood land and trap sediment.
- Desalination gives water in any weather, but uses much energy and makes brine.
- Rainwater harvesting and wetland protection are cheaper and local.
2. Scarcity and demand
- Physical scarcity: not enough water exists, as in dry regions.
- Economic scarcity: water exists, but no money for pipes and treatment.
- Demand grows with population and development: farms use about 70% of freshwater.
3. Saving water and HL ideas
- At home: metering, low-flush toilets, grey-water reuse, rainwater tanks.
- In farming: drip irrigation, drought-tolerant crops, less water-hungry food.
- At HL: water stress (below 1,700 m³ per person a year), transboundary disputes and water footprints.
How it is examined:
| Question | How to score |
|---|---|
| [1] to [2] Identify a trend in water-use data | Quote the figures and the years. |
| [2] to [4] Outline ways to increase supply | Name the method and how it adds water. |
| [4] Distinguish physical and economic scarcity | One line for each, with a named place. |
| [7] Evaluate a water-management strategy | Strengths, limitations and a judgement. |
| [9] Discuss how to achieve water security | Several strategies, named examples, both sides. |
Key terms, one line each:
| Term | In one line |
|---|---|
| Water security | access to enough safe drinking water |
| Physical scarcity | too little water exists for the people who need it |
| Economic scarcity | water exists, but money for supply is lacking |
| Desalination | removing salt from seawater to make freshwater |
| Grey water | used water from sinks and showers, reused for toilets or gardens |
| Water stress | less than 1,700 m³ of clean water per person a year |
| Water footprint | the water used to make a product or by a person or nation |
Last-minute check: answer, then tap to see.
What is the water-stress threshold? Below 1,700 m³ per person per year.
How does water stress differ from scarcity? It also counts quality, access and environmental flows.
Name a transboundary dispute. The Nile: Ethiopia's dam upstream and Egypt downstream.
Has the freshwater planetary boundary been crossed? Yes, for both blue and green water.
Ethiopia began filling the Grand Ethiopian Renaissance Dam on the Blue Nile in 2020. Discuss how a river that crosses borders can cause water stress.
Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
Exam tips
- For a supply method, give a strength and a limitation.
- Say physical or economic scarcity, and name the place.
- In an evaluate, end with a judgement.
- For a dispute, name the river, the countries and the cause.