Water scarcity
Water scarcity is the relative condition in which available water cannot satisfy demand for people, economies, and ecosystems at a particular place and time. It may arise from limited physical supply, declining quality, inadequate infrastructure, weak institutions, or unequal access, and therefore cannot be understood from annual water volume alone.
In simple terms
Scarcity changes with rainfall, storage, water quality, demand, infrastructure, allocation, and governance. Physical scarcity occurs when usable resources are insufficient relative to needs; people may also lack water because systems or institutions do not provide reliable and equitable access. Conditions can be seasonal and local even in a water-rich country. Because water scarcity can contribute to water stress, assessment should consider environmental requirements and who receives water, not only aggregate supply and demand.
Why it matters
Water scarcity can disrupt health, food production, ecosystems, energy, industry, and livelihoods, with poorer or marginalized groups often facing the greatest burden. Understanding its causes determines the response: expanding supply will not correct every allocation, quality, infrastructure, or governance failure. Water stewardship can instead combine demand, access, quality, and ecosystem measures suited to the local cause.
Example
For example, a basin may receive substantial rain annually but experience dry-season scarcity because demand peaks when river flows are low, storage is limited, and pollution reduces usable supply. Responses could combine demand management, leakage repair, fair allocation, pollution control, and protection of environmental flows.
How it differs
Water stress
Water scarcity is the broader condition of insufficient accessible water relative to needs; water stress is commonly measured as withdrawal pressure relative to renewable supply after environmental requirements.