The distribution and importance of fresh water on Earth

Fresh water is a critical resource, yet it constitutes only a small fraction of the total water on Earth.

Breakdown of global water distribution

• Salt water dominance - Approximately 97% of Earth's water is salt water, found in oceans and seas, making it unsuitable for most human uses without treatment.
• Fresh water scarcity - Only 3% of global water is fresh water, with the majority locked away in inaccessible forms:
  • 77% is stored in glaciers and ice sheets.
  • 22% is held as groundwater in soil and rock.
  • 0.5% is available in other forms, including 0.05% in the atmosphere and 0.45% in rivers and lakes.

Significance of fresh water

• Essential for life - Fresh water is vital for the survival of all living organisms, supporting hydration and basic biological functions.
• Key to economic growth - It underpins industrial processes, agricultural productivity, and domestic needs, driving development.
• Uneven distribution - Fresh water availability varies widely, creating 'water-rich' regions with abundant supplies and 'water-poor' areas facing scarcity.

The various uses of fresh water across different sectors

Fresh water serves multiple purposes across different aspects of human life, from personal needs to large-scale economic activities. Its allocation reflects societal priorities and developmental levels.

Categories of fresh water use

• Domestic purposes - Includes activities like bathing, flushing toilets, cooking, drinking, washing clothes and dishes, and garden irrigation.
• Industrial applications - Used in manufacturing processes for goods such as beverages and steel, as well as in generating electricity.
• Agricultural needs - Primarily for irrigating crops to enhance food production and providing drinking water for livestock.
• Leisure activities - Supports recreational pursuits such as fishing in rivers, sailing on lakes, and maintaining sports facilities like golf courses.

Factors driving water demand and consumption patterns

Water demand, often termed consumption, has risen sharply over recent decades due to a combination of population growth and developmental changes. This demand varies significantly between regions based on economic status.

Influences on increasing water demand

• Population growth - The global population has expanded significantly, rising from approximately 5.2 billion in 1990 to around 7.8 billion by 2018, increasing the overall need for water.
• Rising living standards - Development brings improved access to piped water, modern sanitation, appliances like washing machines, and luxuries such as swimming pools, all boosting domestic water use.
• Agricultural expansion - To sustain growing populations, more water is required for irrigation to increase crop yields.
• Industrial growth - Factories and power plants consume large volumes of water for cooling equipment and generating energy, a hallmark of industrialisation.

Contrasts in consumption between developed and developing countries

Individuals in developed countries use approximately 1350 cubic metres of water per year, nearly triple the 420 cubic metres used per person in developing countries. The distribution of water use across sectors differs markedly:

In water-scarcity regions, women often bear the burden of fetching water from distant wells, a physically demanding task that reflects broader gender disparities.

Sources of water supply and their characteristics

Meeting the escalating demand for water requires tapping into various natural and artificial sources. Each source has unique features and challenges associated with its use.

Primary sources of fresh water supply

• Rivers and lakes - Among the earliest sources accessed by humans, these surface water bodies provide readily available fresh water but are susceptible to seasonal fluctuations and pollution.
• Reservoirs - These are man-made lakes formed by constructing dams across valleys, capturing and storing water to ensure a consistent supply, particularly in dry periods.
• Aquifers and wells - Underground water stored in porous rock layers, known as aquifers, is accessed through wells or boreholes. Extraction can involve manual methods like buckets or mechanised pumps, and sometimes water rises naturally under pressure.

Water balance and the global distribution of surplus and deficit areas

The relationship between water demand and supply, known as the water balance, reveals significant global disparities. Mapping these patterns helps identify areas of abundance and scarcity.

Understanding water balance

• Water-deficit areas - Regions where demand outstrips supply, leading to shortages. These are common in arid zones or densely populated, developing areas.
• Water-surplus areas - Locations where supply exceeds demand, often in remote, high-rainfall regions with low population density.
• Water-neutral areas - Places where supply and demand are roughly balanced, maintaining equilibrium.

Global patterns of water availability

• Surplus regions - Limited in number, these include areas like the Amazon basin, central Africa, Southeast Asia, and northern parts of Canada and Russia, often due to high precipitation and low human demand.
• Deficit regions - Widespread in North Africa, the Middle East, central Australia, western USA, and parts of South America, driven by low rainfall or high demand from large populations and development, as seen in countries like India.

Water is moved from surplus to deficit areas using various means, including manual transport in containers, motorised vehicles, tanker ships, and most commonly, extensive pipelines and canals to facilitate large-scale redistribution.