Water scarcity is a condition in which demand for freshwater exceeds the available supply within a particular geographical area and time period, taking into account both quantity and suitability for use. FAO defines water scarcity in terms of insufficient freshwater to meet needs such as drinking, domestic use, irrigation, electricity generation, mining and industry, and notes that pollution can create scarcity when water becomes unsuitable for use. Water scarcity is therefore not simply a situation in which a region receives little rainfall. It can result from physical shortage, excessive demand, pollution, inadequate infrastructure, poor governance, inefficient allocation or combinations of these factors.
Physical water scarcity occurs when there is genuinely insufficient good quality freshwater available to meet demand. It is strongly influenced by climate, rainfall, river discharge, groundwater recharge, evaporation and storage. Arid regions naturally have limited renewable freshwater, but physical scarcity can also develop in wetter regions when populations, agriculture or industry demand more water than rivers and aquifers can sustainably provide. Groundwater can temporarily conceal scarcity because wells may continue producing water even while aquifers are being depleted. Long term physical scarcity therefore depends on the relationship between withdrawals, recharge and environmental water requirements rather than simply the amount of water visible at the surface.
Access scarcity occurs when water exists but people cannot reliably obtain it because of social, institutional, economic or administrative barriers. A community may live near a river or groundwater source while lacking legal rights, financial resources, pumps or safe infrastructure. Unequal allocation can therefore create severe water insecurity even where the physical resource is not globally scarce. Poverty, marginalisation, conflict and weak governance can all restrict access. FAO identifies access scarcity as one of three broad types, alongside physical scarcity and infrastructure scarcity. This distinction demonstrates why water availability and water access are related but not identical concepts.
Infrastructure scarcity occurs when water resources are physically present but infrastructure is insufficient to collect, treat, transport or distribute the water. Examples include communities without reliable pipes, wells, pumps, reservoirs, treatment plants or electricity. A river may contain abundant water during part of the year while households remain water insecure because there is no system capable of storing and delivering safe supplies. Infrastructure scarcity can therefore exist in areas that are not naturally arid. Investment in water infrastructure can improve access, although infrastructure alone does not guarantee sustainability if withdrawals exceed renewable supplies or if water quality is poor.
Agriculture is the largest user of freshwater in many regions, particularly where irrigation is extensive. Irrigated agriculture can increase food production and reduce dependence on rainfall, but it can also place substantial pressure on rivers and aquifers. Industrial processes, electricity generation, mining, livestock production and households add further demand. Population growth and urbanisation can increase municipal demand, while rising consumption levels can increase indirect water use through food, energy and manufactured products. Water scarcity is therefore partly a question of resource availability and partly a question of how societies allocate and use water.
Pollution can create effective water scarcity even where physical quantities remain substantial. Agricultural nutrients and pesticides, industrial chemicals, untreated wastewater, pathogens and other contaminants can make water unsafe for drinking, irrigation or ecosystems. Treatment can restore usability in some cases but requires energy, infrastructure and financial resources. Salinisation is another major problem, particularly in irrigated drylands and coastal aquifers. Excessive groundwater pumping can draw saline water into freshwater aquifers, while evaporation can concentrate salts in poorly drained agricultural soils and water bodies.
Water scarcity can have major effects on food security, public health, ecosystems, economies and migration. Insufficient water can reduce crop yields, livestock productivity and industrial output. Unsafe water increases disease risks, while women and children in some communities can bear disproportionate burdens when water must be collected over long distances. Aquatic ecosystems require environmental flows, so allocating all available water to human uses can damage rivers, wetlands and groundwater dependent ecosystems. FAO emphasises that water scarcity can directly affect human consumption, domestic needs, irrigation, energy generation, mining and industry.
Water scarcity can be reduced through combinations of demand management, efficient irrigation, leakage reduction, wastewater treatment and reuse, rainwater harvesting, groundwater management, reservoir operation, watershed protection, improved agricultural practices and appropriate allocation systems. Desalination can provide freshwater from seawater but generally requires substantial energy and creates concentrated brine that must be managed. Water scarcity should not be treated as a single universal condition because its causes differ between places. FAO's agricultural framework notes that definitions vary and that water scarcity can be understood through the relationship between supply, demand, institutions and the cost of accessing additional water. Sustainable water management therefore requires consideration of quantity, quality, timing, infrastructure, ecosystems and competing human demands.
