Water scarcity occurs when available water supplies cannot adequately satisfy human, economic, agricultural and environmental requirements. Its causes can be divided broadly into physical factors and human factors, although the two frequently interact. Physical causes include low precipitation, high evaporation, prolonged drought, seasonal rainfall, limited natural storage and unfavourable geology. Human causes include population growth, intensive agriculture, industrial demand, inefficient water use, groundwater over abstraction, pollution, inadequate infrastructure and poor water management. Scarcity can therefore occur because there is too little water, because usable water is inaccessible, or because existing supplies are degraded or allocated in ways that leave particular users without reliable access.
Climate is one of the most important physical controls. Arid regions naturally receive little precipitation, while semi arid regions receive enough rainfall for limited vegetation but may still have insufficient reliable water for intensive agriculture and large populations. High temperatures increase evaporation from soils, lakes, reservoirs and vegetation. Drought can temporarily reduce river discharge and groundwater recharge. Seasonal rainfall can create another form of scarcity because a region may receive abundant annual precipitation but have most of it concentrated in a short wet season. The timing of water availability can therefore be as important as the annual total.
Population growth increases water demand for drinking, sanitation, food production, industry and energy. As populations become more urbanised, municipal water systems must supply larger numbers of people and manage greater volumes of wastewater. Rising living standards can also increase per person water consumption through household appliances, landscaping, food production and industrial activity. Population growth does not automatically produce scarcity because technology and infrastructure can increase supply efficiency, but rapid growth in regions with limited renewable resources can create substantial pressure on rivers and aquifers.
Agriculture is a major cause of human induced water scarcity because irrigated crops require large quantities of water. Irrigation can withdraw water from rivers, reservoirs and aquifers, particularly in dry climates where natural rainfall is insufficient for crops. Over pumping groundwater can lower water tables, reduce spring discharge and cause wells to become uneconomic. In coastal areas, excessive groundwater extraction can allow seawater to move inland, producing saltwater intrusion. Agriculture can also degrade water quality through fertilisers, pesticides, salts and animal waste, reducing the amount of water suitable for later use.
Industrialisation can increase water demand through manufacturing, mining, energy production, cooling and processing. Power plants may require large volumes of water for cooling, although the amount consumed depends on technology and whether water is returned to the environment. Mining can alter drainage systems and contaminate surface water or groundwater. Industrial pollutants can make otherwise abundant water unsuitable for drinking, agriculture or ecosystems. Pollution therefore contributes to scarcity by reducing effective supply. Water scarcity is consequently not simply a physical shortage but can also result from the loss of usable water quality.
Infrastructure and governance strongly influence whether people can access available water. A region may have rivers, groundwater or reservoirs but still experience water insecurity if treatment plants, pipelines, wells, storage facilities and distribution systems are inadequate. Leakage from ageing infrastructure can waste substantial quantities of treated water. Poor governance can produce unequal allocation, weak regulation of groundwater extraction, inadequate pollution control or conflict among competing users. Economic water scarcity describes situations where water resources may exist but institutions, investment or infrastructure prevent reliable access for parts of the population.
Environmental degradation can worsen scarcity by reducing the natural systems that store and regulate water. Deforestation can alter infiltration and runoff, while wetland destruction removes natural storage and filtration functions. Soil degradation can reduce infiltration and increase runoff and erosion. Urbanisation replaces permeable ground with roads and buildings, changing recharge and drainage. Climate change can intensify some of these pressures by increasing temperatures and changing precipitation and drought patterns. The resulting effects can reinforce one another, creating feedbacks in which declining water availability increases dependence on groundwater, which then becomes progressively depleted.
Water scarcity is therefore produced by a combination of supply limitations and demand pressures. Physical scarcity may arise from aridity, drought, high evaporation or limited renewable resources, while human induced scarcity can result from overuse, pollution, inefficient infrastructure and inadequate governance. The severity of scarcity depends on the balance between renewable supply and total withdrawals, but also on water quality, seasonal reliability, environmental flow requirements and social access. Addressing scarcity consequently involves demand management, efficient agriculture, pollution prevention, groundwater protection, infrastructure investment, water reuse, conservation and adaptation to climatic variability rather than relying on a single technical solution.
