Cambridge Syllabus Notes

Water Resources and Management (Cambridge 9696)

Learning Objective

Explain how water resources are managed by increasing supply, managing demand and addressing the challenges to sustainable water security. Use the global pattern of water resources, the human water cycle and detailed case‑study evidence to evaluate the effectiveness and trade‑offs of different strategies.

1. Global Pattern of Water Resources

Surface water – rivers (≈ 2 % of Earth’s water), lakes and reservoirs.
Groundwater – aquifers in porous rocks and sediments (≈ 30 % of fresh water).
Ice‑sheet & glacier water – Antarctica, Greenland and high‑altitude glaciers (≈ 68 % of fresh water, but largely unavailable for direct use).
Atmospheric water – water vapour and precipitation; the source of all usable water.

2. The Human Water Cycle

Suggested diagram: “Human water cycle” – capture → use → disposal → reuse/recycle.

Capture – abstraction from rivers, lakes, reservoirs, groundwater or rainwater harvesting.
Use – domestic, industrial, agricultural and environmental (ecological flow) purposes.
Disposal – wastewater (sewage, industrial effluent) and solid waste.
Reuse / Recycling – treatment for reuse in irrigation, industry or indirect potable reuse.

3. Trends in Water Consumption

Global freshwater withdrawals have risen from ~ 2 000 km³ yr⁻¹ (1970) to > 4 000 km³ yr⁻¹ (2020).
Per‑capita use varies widely:
- ≈ 1 500 L person⁻¹ day⁻¹ in high‑income countries.
- ≈ 300 L person⁻¹ day⁻¹ in low‑income countries.
Water‑use intensity (m³ per US $ GDP) generally falls as economies develop, but total demand continues to grow because of population increase and urbanisation.

4. Water‑Stress vs. Water‑Scarcity

Concept	Definition (Cambridge)	Key Indicator
Water‑stress	When annual water withdrawals exceed 25 % of the renewable freshwater resources of a region.	Withdrawal ÷ Renewable supply × 100 % > 25 %.
Physical water‑scarcity	When renewable supply is insufficient to meet all demands, even with perfect management.	Renewable supply < Demand.
Economic water‑scarcity	When water is physically available but cannot be accessed because of lack of infrastructure, investment or institutional capacity.	Low per‑capita supply despite adequate renewable resources.

5. Physical and Human Controls on Supply and Demand

Control	Influence on Supply	Influence on Demand
Climate (precipitation, temperature)	Determines runoff, recharge and seasonal availability.	Sets irrigation requirements and domestic consumption patterns.
Geology & Relief	Controls groundwater storage capacity and river gradients.	Influences feasibility of wells, dams and flood‑control structures.
Population & Urbanisation	Creates new abstraction points and pressure on catchments.	Raises per‑capita domestic demand and wastewater volumes.
Infrastructure (pipes, treatment plants, irrigation systems)	Enables capture and storage (e.g., reservoirs, recharge basins).	Determines delivery efficiency and loss (leakage, evaporation).
Policy & Institutional Arrangements	Allocation licences, water‑rights, trans‑boundary agreements.	Pricing, water‑use regulations, sectoral priorities.

6. Strategies to Increase Water Supply

Method	Key Features & Examples	Evaluation (Benefits / Limitations)
Surface‑water development	• Dams & reservoirs – Three Gorges Dam (China). • Inter‑basin transfers – South–North Water Transfer (China); California State Water Project (USA).	Benefits: Large, reliable storage; flood control; hydro‑electric power. Limitations: High capital cost; ecological disruption (sediment trapping, habitat loss); displacement of people; evaporation losses in hot climates.
Groundwater development	• Deep boreholes & pumped wells – Arabian Peninsula. • Artificial recharge – infiltration basins, Managed Aquifer Recharge (California).	Benefits: Often less visible, can supply remote areas; provides drought buffer. Limitations: Over‑extraction → falling water tables, land subsidence, salinisation; recharge projects need suitable geology and water quality.
Desalination	• Thermal distillation – Ras Al‑Khaimah (UAE). • Reverse osmosis – Jebel Ali (Saudi Arabia); Sorek (Israel).	Benefits: Provides water where freshwater is scarce; predictable output. Limitations: Energy‑intensive (often fossil‑fuel powered → high carbon footprint); brine disposal can damage marine ecosystems; high operating cost.
Rainwater harvesting & small‑scale storage	• Rooftop systems – semi‑arid India and Kenya. • Check‑dams (“johads”) and percolation ponds – Murray‑Darling Basin (Australia); Rajasthan (India).	Benefits: Low cost; enhances groundwater recharge; community‑managed. Limitations: Dependent on rainfall variability; limited volume; requires regular maintenance.

7. Strategies to Manage Water Demand

Approach	Key Measures & Examples	Evaluation (Effectiveness / Trade‑offs)
Economic Instruments	• Increasing block tariffs – South Africa (2000s). • Abstraction charges for agriculture – Murray‑Darling Basin water market.	Effectiveness: Users reduce consumption when price rises. Trade‑offs: May burden low‑income households; requires reliable metering and billing.
Technological Measures	• Low‑flow fixtures – dual‑flush toilets, aerated taps. • Efficient irrigation – drip (Israel, California) and sprinkler with scheduling. • Industrial water recycling – closed‑loop cooling in Japanese steel plants.	Effectiveness: Can achieve 20‑50 % water savings. Trade‑offs: Capital outlay; need for user training and maintenance.
Behavioural & Institutional Measures	• Public awareness campaigns – World Water Day; Singapore “Save Water”. • Regulatory limits on water‑intensive crops – cotton restrictions in Australia’s dry zones. • Leak detection & repair programmes – London Water (2015‑2020).	Effectiveness: Often low‑cost; can achieve 5‑15 % reductions. Trade‑offs: Behaviour change is slow; sustained education and enforcement are required.

8. Water Security

Definition (Cambridge 9696): The capacity of a population to obtain sufficient, safe water of acceptable quality for sustaining livelihoods, health and the environment, now and in the future.

Global distribution (approx. 2020):

Region	Water‑secure (%)	Water‑insecure (%)
North America & Europe	≈ 90	≈ 10
East Asia & Pacific	≈ 70	≈ 30
Sub‑Saharan Africa	≈ 30	≈ 70
Middle East & North Africa	≈ 25	≈ 75
Latin America & Caribbean	≈ 80	≈ 20

Access issues – poverty, inadequate infrastructure, pollution and governance gaps can prevent secure water even where physical resources exist.

9. Challenges, Trade‑offs and Sustainable Management

Challenge	Impact on Water Resources	Typical Mitigation / Management Response	Key Trade‑off
Climate Change	More extreme droughts, altered runoff timing, sea‑level rise (coastal salinisation).	Adaptive reservoir operation, climate‑resilient crop varieties, flexible storage.	Greater storage can increase evaporation losses and ecological disruption.
Population Growth & Urbanisation	Higher domestic and industrial demand; larger wastewater loads.	Integrated urban water management, water‑recycling schemes, smart‑metering.	High capital cost for treatment and distribution upgrades.
Water Pollution	Reduced usable supply; health risks.	Strict effluent standards, catchment‑scale pollution control, nature‑based solutions (wetlands).	Regulation may increase production costs for industry and agriculture.
Over‑extraction of Groundwater	Falling water tables, land subsidence, salinisation.	Groundwater licensing, artificial recharge, conjunctive use with surface water.	Licensing can be politically sensitive; recharge projects need suitable land.
Institutional Fragmentation	Conflicting sectoral policies; inefficient allocation.	River‑basin organisations, Integrated Water Resources Management (IWRM), water‑rights markets.	Creating basin authorities may require legislative change and stakeholder buy‑in.
Trans‑boundary Water Issues	Shared rivers can become sources of conflict (e.g., Nile, Indus, Mekong).	International treaties, joint‑management commissions, data‑sharing protocols.	Negotiations can be lengthy; power imbalances affect outcomes.

10. Detailed Case Study – Cape Town “Day Zero” (South Africa)

This example follows the syllabus requirement to present prediction, causes, impacts and evaluation of a water‑management situation.

Prediction (2017‑2018) – City planners forecast that, without drastic cuts, reservoir levels would fall below 13 % of capacity by April 2018, triggering “Day Zero” – the shutdown of municipal taps.
Causes
- Extended drought (2015‑2017) – 60 % below average rainfall in the Western Cape catchments.
- Rapid population growth and tourism‑driven demand (≈ 1 % yr⁻¹).
- High per‑capita domestic consumption (≈ 250 L person⁻¹ day⁻¹) and limited water‑saving infrastructure.
Impacts
- Severe water‑stress – 5 000 ha of agricultural land fell out of production.
- Economic loss estimated at US$ 1.5 bn (tourism, agriculture, lost productivity).
- Social impacts – restrictions on household use, school closures for hygiene, heightened public anxiety.
Management Response
- Demand‑side: aggressive water‑saving campaign, tiered water tariffs, mandatory 50 % reduction in household use, installation of low‑flow devices.
- Supply‑side: temporary desalination pilot (30 000 m³ day⁻¹), groundwater extraction from the Table Mountain aquifer, and storm‑water capture.
- Institutional: establishment of a city‑wide water‑management task force and real‑time public dashboards.
Evaluation
- Successes – Household consumption fell 50 % within weeks; reservoirs stabilised above 30 % capacity; “Day Zero” was avoided.
- Limitations – Heavy reliance on behavioural change; long‑term supply remains vulnerable to future droughts; desalination pilot was costly and energy‑intensive.
- Lesson for the syllabus – Demonstrates that demand‑side measures can be more rapid and cost‑effective than large‑scale supply projects, but sustained investment in diversified supply (e.g., renewable‑energy‑powered desalination, managed aquifer recharge) is needed for long‑term security.

11. The Water Balance Equation in Management

For any catchment the water balance is expressed as:

P = E + R + ΔS

P – Precipitation (input).
E – Evapotranspiration (loss to the atmosphere).
R – Runoff (surface water leaving the catchment).
ΔS – Change in storage (soil moisture, groundwater, reservoirs).

Managers manipulate ΔS (e.g., by building reservoirs or recharging aquifers) and influence E (e.g., through afforestation) to balance supply and demand under changing P.

12. Summary Checklist for the Exam

Describe the global distribution of water resources and the human water cycle.
Explain water‑stress, physical scarcity and economic scarcity, using the appropriate indicators.
Identify the main physical and human controls on supply and demand.
Outline at least two supply‑side and two demand‑side strategies, giving concrete examples.
Define water security and discuss its spatial variation.
Analyse a detailed case study, covering prediction, causes, impacts and evaluation of the management response.
Discuss the major challenges (climate change, population growth, pollution, over‑extraction, institutional issues, trans‑boundary conflicts) and the trade‑offs involved in their mitigation.

Management of water resources: increasing supply, managing demand, challenges, detailed examples