Key Idea: Most marks in topic 4.2 come from increasing supplies and water scarcity. Learn those first, then growing demand and saving water.
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
- At home: metering, low-flush toilets, grey-water reuse, rainwater tanks.
- In farming: drip irrigation, drought-tolerant crops, less water-hungry food.
- Water security means enough safe drinking water for everyone.
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 |
Last-minute check: answer, then tap to see.
Physical or economic scarcity: no pipes in a rainy country? Economic scarcity.
Which sector uses the most freshwater? Agriculture, about 70%.
One drawback of desalination? High energy use, or brine harming sea life.
Name two ways to save water at home. Any two: metering, low-flush toilets, grey water, rain tanks.
IB-style questionEvaluate[4 marks]
Israel gets much of its drinking water from desalination plants on its coast. Evaluate desalination as a way to increase water supply.
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.
- Quote numbers from the data, with units.