Water: global supply, insecurity and sustainable supply schemes

About 2 billion people lack safely managed drinking water (WHO 2023). Demand is projected to rise 55 % by 2050. Climate change is intensifying both droughts and floods. Water security has become a defining challenge of the 21st century.

Global water consumption

• 70 % for agriculture (irrigation)
• 20 % for industry (cooling, processing)
• 10 % for domestic use (drinking, washing, cooking)

A US household uses about 380 L/person/day; many in sub-Saharan Africa survive on under 20 L. The UN considers <50 L/person/day water-stressed.

Factors affecting water availability

• Climate — arid zones receive <250 mm rain/year. Climate change is worsening Sahel droughts and Indian monsoon variability.
• Geology — porous rocks (chalk, sandstone) form aquifers that store water; impermeable rocks force runoff.
• Pollution — sewage, industrial waste, fertilisers and farm runoff. India's Ganges receives 1 bn L/day untreated.
• Over-abstraction — California's Central Valley aquifer falling 1 m/year; sinking land in Mexico City.
• Poverty — can't afford treatment, household connection or pumps.
• Limited infrastructure — rural Africa: women walk avg 6 km/day to collect water.

Water insecurity — impacts

• Disease — diarrhoea kills 500 000 children/year from unsafe water.
• Reduced productivity — water collection takes time/energy, especially women's.
• Food insecurity — drought devastates harvests (Somalia, Ethiopia).
• Conflict — Nile dispute between Egypt and Ethiopia (Grand Ethiopian Renaissance Dam, GERD); Israel–Palestine water access.
• Migration — climate refugees fleeing drying farmland.

Strategies to increase water supply

1. Diverting supplies (water transfer)

Move water from surplus regions to deficit. South–North Water Transfer Project, China — transfers Yangtze water to Beijing/Tianjin via 1 432 km of canals; world's largest scheme; cost ~$80 bn.

2. Dams and reservoirs

Store water for dry seasons. Three Gorges (China), Aswan High Dam (Egypt). Drawback: silt build-up, displaced people.

3. Desalination

Removes salt from sea/brackish water. Saudi Arabia produces 50 % of its drinking water by desalination. Energy-intensive — significant carbon footprint unless powered by renewables.

4. Water recycling and reuse

Singapore's NEWater — treated wastewater meets 40 % of demand. Drip irrigation used in Israel cuts agricultural water use 40 %.

Large-scale water-supply scheme case study — Lesotho Highlands Water Project

A multi-decade scheme transferring water from Lesotho (mountainous, water-rich) to South Africa's industrial heartland (Gauteng).

• Scale: 5 large dams, 200 km of tunnels.
• Cost: $4 bn+.
• Successes: Gauteng (8 m people) reliable water; Lesotho earns $50 m/yr royalties; hydroelectric power for Lesotho.
• Failures: 30 000 farmers displaced; 17 sites of cultural significance flooded; downstream rivers reduced to trickles; Lesotho's poverty rate barely changed.

Sustainable water supply

• Conservation — low-flow taps, rainwater harvesting, grey-water reuse, water meters.
• Pricing reform — tiered pricing penalising heavy use.
• Efficient irrigation — drip irrigation can save 40–60 % vs flood irrigation.
• Restoring catchments — reforesting hillsides reduces erosion and recharges aquifers.
• Wastewater treatment — Singapore's NEWater is the gold standard.
• Behaviour change — shorter showers, fixing leaks.

Examiner tips

• Always pair scheme name with statistics (Lesotho 5 dams, $50 m/yr royalties).
• Evaluate trade-offs — most large schemes have winners (cities, industry) and losers (displaced farmers, downstream ecosystems).
• Sustainability is increasingly the higher-mark answer — name NEWater Singapore or Israeli drip irrigation as flagship sustainable approaches.