Water: Global Supply & Management

Water is essential for life, agriculture, industry, and sanitation — yet it is one of the most unevenly distributed resources on Earth. This lesson examines global patterns of water supply and demand, the causes and consequences of water insecurity, and the large-scale strategies used to manage and increase water supply. This is a core part of the AQA GCSE Geography specification.

---

The Global Water Crisis

Key Statistics

• 71% of the Earth's surface is covered by water, but only 2.5% is freshwater
• Of that freshwater, about 69% is locked in ice caps and glaciers
• Only about 0.3% of the world's total water is accessible surface freshwater (rivers, lakes, swamps)
• Approximately 2.2 billion people lack access to safely managed drinking water
• By 2025, half the world's population could be living in water-stressed areas

Water Surplus and Deficit

Condition	Definition	Examples
Water surplus	Supply exceeds demand	Canada, Russia, Scandinavia, Brazil
Water deficit	Demand exceeds supply	North Africa, Middle East, parts of India and China
Water stress	High demand relative to supply (below 1,700 m³ per person per year)	South Africa, parts of the USA, Mediterranean
Water scarcity	Critically insufficient water (below 1,000 m³ per person per year)	Libya, Yemen, Jordan, parts of Pakistan

---

Factors Affecting Water Availability

Physical Factors

Factor	Explanation
Climate	Equatorial regions receive heavy, reliable rainfall; arid regions (20°–30° N and S) receive very little
Geology	Permeable rocks (chalk, limestone) store water in aquifers; impermeable rocks cause surface runoff
Drainage	Major river basins (Amazon, Congo, Ganges) provide reliable surface water
Seasonal variation	Monsoon climates have extreme wet and dry seasons
Glaciers and snowmelt	Many rivers (e.g. Indus, Ganges, Rhône) depend on meltwater from glaciers and snowpack

Human Factors

Factor	Explanation
Population growth	More people means more demand for drinking water, sanitation, and agriculture
Urbanisation	Cities concentrate demand and often require water to be transferred long distances
Industrialisation	Factories and power plants use large volumes of water for cooling and processing
Agriculture	Irrigation accounts for approximately 70% of all freshwater withdrawals globally
Pollution	Industrial discharge, agricultural runoff, and sewage contaminate freshwater sources
Over-abstraction	Pumping groundwater faster than it is replenished lowers water tables
Deforestation	Reduces interception and transpiration, altering the water cycle

Exam Tip: When answering questions about water availability, always address both physical and human factors. A strong answer connects them — e.g., "Although Brazil receives heavy equatorial rainfall (physical), rapid deforestation of the Amazon (human) is disrupting the regional water cycle."

---

Water Consumption by Sector

Different sectors use water in very different ways:

Sector	% of Global Freshwater Use	Key Uses
Agriculture	~70%	Irrigation of crops, livestock watering
Industry	~20%	Cooling, processing, cleaning, manufacturing
Domestic	~10%	Drinking, cooking, washing, sanitation

In HICs, industrial and domestic use is proportionally higher. In LICs, agriculture dominates water consumption.

---

Strategies to Increase Water Supply

Dams and Reservoirs

Dams are one of the most common methods of managing water supply. They store water behind a barrier for use during dry periods and can also generate hydroelectric power.

Advantages: reliable water supply, flood control, hydroelectric power generation, recreation and tourism

Disadvantages: expensive to build, displace communities, trap sediment (reducing downstream fertility), alter river ecosystems, risk of failure

Water Transfer Schemes

Water transfer schemes move water from areas of surplus to areas of deficit, often through aqueducts, pipelines, or canals.

Examples:

• China's South-North Water Transfer Project — the world's largest, transferring water from the Yangtze River basin to the arid north
• Libya's Great Man-Made River — a network of pipes bringing fossil water from underground aquifers in the Sahara to coastal cities
• Kielder Water, UK — transfers water from Northumberland to the north-east of England

Desalination

Desalination removes salt from seawater or brackish water to produce freshwater.

Feature	Detail
Methods	Reverse osmosis, distillation
Major users	Saudi Arabia, UAE, Israel, Australia, Spain
Advantages	Provides freshwater in arid regions with limited alternatives
Disadvantages	Very energy-intensive, expensive, produces concentrated brine waste that harms marine ecosystems

Groundwater Extraction

Pumping water from underground aquifers using boreholes and wells:

• Many of the world's largest aquifers are being over-abstracted (e.g. the Ogallala Aquifer in the USA, the North China Plain aquifer)
• Over-abstraction leads to falling water tables, land subsidence, and saltwater intrusion in coastal areas

---

Case Study: The Lesotho Highlands Water Project (LHWP)

The Lesotho Highlands Water Project is a large-scale water transfer scheme that diverts water from the highlands of Lesotho to the water-scarce Gauteng Province of South Africa (which includes Johannesburg and Pretoria).

Background

Feature	Detail
Location	Lesotho (mountainous kingdom surrounded by South Africa)
Partners	Lesotho and South Africa — joint venture
Phase 1	Completed 1998 — Katse Dam and transfer tunnel
Phase 2	Under construction — Polihali Dam
Water transferred	Billions of litres per year via tunnels through the mountains

How It Works

• Lesotho receives abundant rainfall and snowmelt in its highlands
• A series of dams (Katse Dam, Mohale Dam) store water
• Transfer tunnels carry water through the Maluti Mountains to the Vaal River system in South Africa
• South Africa pays Lesotho royalties for the water — a significant source of national income

Advantages

Benefit	Explanation
Water supply	Provides reliable water to Gauteng, home to over 15 million people
Revenue for Lesotho	Water royalties are a major source of income for one of Africa's poorest countries
Hydroelectric power	The dams generate electricity for Lesotho, improving energy security
Employment	Construction and maintenance provide jobs in Lesotho
Flood control	The dams help regulate river flow and reduce downstream flooding

Disadvantages

Concern	Explanation
Displacement	Thousands of people were relocated to make way for dams and reservoirs
Environmental impact	Ecosystems submerged; downstream river flows altered
Compensation disputes	Some displaced communities argue they received inadequate compensation
Corruption	The project has been marred by corruption scandals involving bribes
Dependency	Lesotho's economy becomes dependent on water royalties from South Africa
Climate change	Reduced rainfall could undermine the long-term viability of the project