Water Uses, Demand & Supply

Three main uses of water by people are:

• Agriculture — irrigating crops (rice, cotton, maize) and watering livestock.
• Industry — cooling power stations, washing and chemical processing in factories.
• Domestic / human hygiene — drinking, cooking, washing, sanitation in homes.

(Leisure — swimming pools, golf courses, water sports — is also accepted.)

• Water shortage — a situation in which demand for water exceeds supply, leading to scarcity, rationing or competition for water resources.

• Water surplus — a situation in which supply of water exceeds demand, so water is plentiful relative to local needs.

Three drivers have caused global water demand to rise dramatically.

First, population growth: world population has grown from about 1.6 billion in 1900 to ~8 billion today, multiplying the demand for drinking water, cooking, washing and sanitation.

Second, agricultural expansion and irrigation: more land has been cultivated to feed the growing population, and irrigation now provides ~70% of global fresh-water withdrawals. Yields per hectare have also risen, but only through more water-intensive farming.

Third, industrialisation and rising per-capita consumption: industrial cooling, washing and processing have all expanded with economic growth. In developed countries, affluence has driven up per-capita domestic use through dishwashers, washing machines, showers, swimming pools and lawns.

Several factors interact to produce water shortage.

Climate is often the starting point: regions with low rainfall (the Sahel, Middle East, Australia's interior) and high evapotranspiration (hot, dry climates) have small natural supply. Rainfall may also be highly seasonal, so a few wet months must support a whole year of demand.

Population growth and urbanisation push demand up in regions that may already be marginal. The Middle East has the world's highest population growth in some water-stressed states (Egypt, Yemen, Saudi Arabia). Rapid urban growth concentrates demand in cities where local supply cannot meet it (e.g. Cape Town's "Day Zero" crisis 2017–18).

Over-use and poor management can deplete supplies even where natural water exists. Massive irrigation from the Aral Sea's feeder rivers (Amu Darya, Syr Darya) for cotton farming has shrunk the lake by ~90%. The Colorado River often fails to reach the Gulf of California because of upstream abstraction. Inefficient water use (flood irrigation, leaks in old pipes, low water-pricing) magnifies the problem.

Climate change is now intensifying shortage in many already-stressed regions (Mediterranean, south-west USA).

The distribution of water shortage and surplus is fundamentally uneven because the natural distribution of precipitation and the human distribution of demand do not match.

Water-surplus regions typically combine high precipitation with low population density and limited industrial / agricultural demand. The Amazon basin (Brazil) receives ~2,000–3,000 mm/year of rainfall and is sparsely populated outside its cities. Scandinavia, the Canadian Shield, and parts of New Zealand show similar profiles. Renewable freshwater per capita exceeds 50,000 m³/year in these regions.

Water-shortage regions combine low precipitation, high evapotranspiration and / or high population density. The Middle East (Saudi Arabia, UAE, Israel) has rainfall under 200 mm/year and population growth, so per-capita renewable water is under 1,000 m³/year — below the World Bank "water scarcity" threshold. Per-capita water in Kuwait and Saudi Arabia is under 500 m³/year, 100 times less than in countries like Iceland or Suriname. The Sahel and parts of South Asia face similar pressure.

This unevenness is widening:

• Population growth concentrates in already-water-stressed regions (Africa, South Asia).
• Climate change is making dry areas drier (south-west USA, Mediterranean) and wet areas wetter (south-east Asia monsoon).
• Agricultural intensification competes with domestic supply in emerging economies (India, China).

The gap can be partially closed by management (desalination — Saudi Arabia, UAE; water transfer — China's South-North scheme; drip irrigation — Israel), but at high cost. The fundamental unevenness remains.

Physical water scarcity occurs where there is GENUINELY NOT ENOUGH water in the environment to meet demand. Economic water scarcity occurs where water IS physically available but people lack the infrastructure, income or institutions to access it. These two conditions arise from very different geographies and call for very different responses.

Physical water scarcity — Saudi Arabia and the Arabian Gulf states. The Arabian peninsula is characterised by extreme aridity: rainfall under 100 mm/year across most of Saudi Arabia and the UAE, intense solar radiation driving very high evapotranspiration, no major perennial rivers, and limited shallow groundwater. Per-capita renewable freshwater in Saudi Arabia is under 80 m³/year — well below the World Bank "absolute scarcity" threshold of 500 m³/year. Kuwait's figure is just ~6 m³/year. These countries are wealthy enough to afford expensive solutions: DESALINATION provides ~80% of UAE drinking water; deep FOSSIL AQUIFERS (water laid down during wetter Pleistocene climates) supply non-renewable groundwater. Israel uses drip irrigation to maximise efficiency and recycles ~85% of wastewater for agriculture. The geography is fundamental — climate dictates that no amount of investment in pipes will fix the underlying shortage; new SOURCES of water (desalination, recycling) are essential.

Economic water scarcity — rural sub-Saharan Africa. Much of sub-Saharan Africa (Mozambique, Malawi, DRC, parts of Ethiopia and Tanzania) actually receives ADEQUATE rainfall on average and has flowing rivers and accessible groundwater. The problem is that INFRASTRUCTURE to capture, treat and distribute water is absent or inadequate. Wells need drilling and maintenance; pipelines are limited or non-existent in rural areas; sewage treatment is rare; pumping requires electricity that may be unreliable; institutional capacity to manage water resources is weak. The result is that millions of people walk hours daily to collect water from unsafe sources. >40% of people in sub-Saharan Africa lack access to safely-managed drinking water (WHO). The geography of economic scarcity is therefore a geography of POVERTY and INSTITUTIONAL CAPACITY, not climate.

Mixed cases. India and Pakistan illustrate that the two types can occur together. Northern India has high rainfall (monsoon) but rural areas suffer economic scarcity from inadequate infrastructure; meanwhile the agricultural Punjab faces PHYSICAL scarcity from groundwater over-pumping that has lowered the water table by tens of metres. China faces physical scarcity in the dry north (driving the South-North Water Transfer) but economic scarcity in poorer rural provinces.

Why the distinction matters for management.

• Physical scarcity requires supply-side solutions: desalination, fossil-aquifer abstraction, water transfer schemes, recycling.
• Economic scarcity requires investment-side solutions: drilling wells, building treatment works, financing pipelines, institutional capacity-building, NGO-supported small-scale technology (sand dams, rainwater harvesting).

Building a desalination plant in Mozambique wouldn't help much — the existing river water cannot reach people. Drilling wells in Kuwait wouldn't help much either — there's no fresh groundwater to extract.

Assessment. The two types of scarcity have different geographical origins: physical scarcity follows arid climates and limited natural supply; economic scarcity follows POVERTY and INSTITUTIONAL WEAKNESS. Climate, geology and demography set the natural supply; economic and institutional capacity determine whether that supply can be accessed. Effective water management must DIAGNOSE which type a region faces before choosing solutions — confusing the two is one of the most common policy mistakes in international water development.

Climate change is undoubtedly a major and growing threat to global water supply, but several other threats compete for the "most important" designation, and the answer depends on time-scale and geographical context.

The case for climate change. Climate change affects water supply through several mechanisms:

• Changing precipitation patterns. Dry regions are getting DRIER (the Sahel, Mediterranean, south-west USA, parts of southern Africa); wet regions are seeing more INTENSE precipitation (south-east Asia monsoons, north-west Europe winters). The closed-system total is unchanged, but the local distribution is shifting in ways that hurt many already-vulnerable populations.
• Glacier retreat. Himalayan glaciers feed rivers (Indus, Ganges, Brahmaputra, Mekong) that supply ~1.5 billion people. As glaciers shrink, summer river flow will eventually FALL after a brief peak. The Andean glaciers supply La Paz, Quito and Lima similarly. The Alps feed the Rhône and Rhine.
• Sea-level rise threatens deltaic populations (Bangladesh, Nile delta, Pearl River delta) directly and contaminates coastal groundwater with saltwater intrusion.
• Increased evaporation losses in hot regions reduce river discharge and groundwater recharge.
• Extreme events — droughts (south-east Australia, California, Cape Town's "Day Zero" 2017-18) and floods (Bangladesh, Pakistan 2022) — disrupt supply unpredictably.

The 2022 IPCC report concludes that water-related impacts are among the most severe consequences of warming. The threat is GLOBAL, INCREASING and partly IRREVERSIBLE.

The case for other threats being equally or more important.

1) Population growth and rising demand. Global population has gone from ~1.6 billion (1900) to ~8 billion (today), projected to ~10 billion by ~2050. Even with no climate change, rising population — concentrated in already-water-stressed regions like sub-Saharan Africa, South Asia and the Middle East — would push many regions into scarcity. Population growth has caused most of the historic water-stress increase to date.

2) Agricultural intensification. Irrigation has tripled since 1950 and now uses ~70% of global withdrawals. As emerging economies adopt meat-rich diets (1 kg of beef ≈ 15,000 L of virtual water), agricultural water demand is forecast to keep rising. This driver may be MORE IMPACTFUL than climate change in the short term.

3) Pollution. Water that is contaminated by sewage, industry or agriculture is effectively REMOVED from useful supply. Yamuna (India) receives ~3 billion litres of mostly untreated sewage daily; the river is biologically dead through Delhi. Pollution can wipe out supply faster than climate change drains it.

4) Over-abstraction. Groundwater depletion in India's Punjab and California's Central Valley is depleting aquifers built over millennia. The Aral Sea has lost 90% of its volume from over-abstraction unrelated to climate. The Colorado River often fails to reach the Gulf because of upstream withdrawals.

5) Institutional and economic weakness (economic water scarcity). In much of sub-Saharan Africa, lack of infrastructure is a bigger short-term threat to safe water supply than climate change.

6) Political conflict. Water-stressed regions also tend to be politically unstable (Yemen, Syria, parts of Central Asia). Conflict can destroy water infrastructure or block access for years.

Counter-argument: climate change AMPLIFIES all other threats. Even if rising demand is the "biggest" driver today, climate change is the THREAT MULTIPLIER. It makes pollution worse (lower flows concentrate pollutants), makes over-abstraction more dangerous (less rainfall to recharge), makes economic scarcity harder to fix (more unstable flows to plan against), and intensifies political tension over water resources.

Judgement. No single threat is universally "most important". Over the SHORT TERM (next 10-20 years), rising demand, pollution and over-abstraction may individually do more damage than climate change in many regions. Over the LONGER TERM (2050+), climate change will be the dominant background driver that determines whether other threats are manageable or catastrophic. Climate change is also UNIVERSAL — it affects every region of the world — while other threats are more localised. In a SPECIFIC region (Bangladesh's deltaic flood + sea-level rise) climate change may indeed be the most important threat; in another (rural Mozambique) economic scarcity dominates. The honest answer is that climate change is the THREAT MULTIPLIER and the long-term BACKGROUND DRIVER, but it interacts with — and is sometimes outweighed by — other simultaneous threats. The 21st-century water-supply challenge requires addressing ALL of them in a coordinated way.

Agreement. Population growth IS a fundamental driver: more people require more water for drinking, cooking, washing and sanitation. Global population has gone from ~1.6 billion (1900) to ~8 billion today — a fivefold increase. Population growth is also concentrated in already water-stressed regions (sub-Saharan Africa, the Middle East, parts of South Asia), so it compounds the local pressure.

Disagreement / other factors. Demand per person matters as much as population numbers.

• Agricultural intensification — to feed the larger population, irrigated agriculture has tripled since 1950 and now uses ~70% of global withdrawals. Even at constant population, this would have raised demand sharply.
• Industrialisation — rapidly growing economies (China, India, Brazil) have added massive industrial water use (cooling, processing).
• Rising affluence — in developed (and increasingly emerging) economies, per-capita domestic water use has risen through showers, dishwashers, washing machines, swimming pools, golf courses. The average American uses ~5–10 times the water of someone in Mozambique.
• Diet change — meat-rich diets are very water-intensive (1 kg of beef = ~15,000 litres). Rising meat consumption in China and India magnifies agricultural water demand far beyond population growth.

Judgement. Population growth alone would have raised demand, but only modestly. The much bigger driver is the COMBINATION of population growth WITH agricultural intensification, industrialisation and rising per-capita consumption. Population is necessary but not sufficient — affluence and changing demand patterns are equally important.