Water scarcity
Water scarcity is the lack of any, local or economically viably transportable, sources of fresh water resources to meet the standard water demand in a region. There are two types of water scarcity. One is physical. The other is economic water scarcity. Physical water scarcity is where there is not enough water to meet all demands. This includes water needed for ecosystems to function. Regions with a desert climate often face physical water scarcity. Central Asia, West Asia, and North Africa are examples of arid areas. Economic water scarcity results from a lack of investment in infrastructure or technology to draw water from rivers, aquifers, or other water sources. It also results from weak human capacity to meet water demand. Many people in sub-Saharan Africa are living with economic water scarcity.
There is and has always been enough physical supply of freshwater for current or near or distant future demand in a global scale. As such, water scarcity is caused by a mismatch between when and where people need water, and when and where it is available. This can happen due to an increase in the number of people in a region, changing living conditions and diets, and expansion of irrigated agriculture. Climate change, deforestation, water pollution and wasteful use of water can also mean there is not enough water. These variations in scarcity may also be a function of prevailing economic policy and planning approaches.
Water scarcity assessments look at many types of information. They include green water, water quality, environmental flow requirements, and virtual water trade. Water stress is one parameter to measure water scarcity. It is useful in the context of Sustainable Development Goal 6. Half a billion people live in areas with severe water scarcity throughout the year, and around four billion people face severe water scarcity at least one month per year. Half of the world's largest cities experience water scarcity. There are 2.3 billion people who reside in nations with water scarcities.
There are different ways to reduce water scarcity. It can be done through supply and demand side management, cooperation between countries and water conservation. Expanding sources of usable water can help. Reusing wastewater and desalination are ways to do this. Others are reducing water pollution and changes to the virtual water trade.
Definitions
Water scarcity has been defined as the "volumetric abundance, or lack thereof, of freshwater resources" and it is thought to be "human-driven". This can also be called "physical water scarcity". There are two types of water scarcity. One is physical water scarcity and the other is economic water scarcity. Some definitions of water scarcity look at environmental water requirements. This approach varies from one organization to another. Related concepts are water stress and water risk. The CEO Water Mandate, an initiative of the UN Global Compact, proposed to harmonize these in 2014. In their discussion paper they state that these three terms should not be used interchangeably.Some organizations define water stress as a broader concept. It would include aspects of water availability, water quality and accessibility. Accessibility depends on existing infrastructure. It also depends on whether customers can afford to pay for the water. Some experts call this economic water scarcity.
The FAO defines water stress as the "symptoms of water scarcity or shortage". Such symptoms could be "growing conflict between users, and competition for water, declining standards of reliability and service, harvest failures and food insecurity". This is measured with a range of Water Stress Indices.
A group of scientists provided another definition for water stress in 2016: "Water stress refers to the impact of high water use relative to water availability." This means water stress would be a demand-driven scarcity.
In a 2026 report, the UNU Institute for Water, Environment and Health says that the terms “water stressed” and “water crisis” fail to reflect today’s reality in many places, arguing that " are no longer adequate to spark proper responses as they cannot explain what is happening today in human-water systems", and instead advocates for the use of the term water bankruptcy "to refer to this new reality, not for rhetorical escalation, but for diagnostic clarity".
Types
Experts have defined two types of water scarcity. One is physical water scarcity. The other is economic water scarcity. These terms were first defined in a 2007 study led by the International Water Management Institute. This examined the use of water in agriculture over the previous 50 years. It aimed to find out if the world had sufficient water resources to produce food for the growing population in the future.Physical water scarcity
Physical water scarcity occurs when natural water resources are not enough to meet all demands. This includes water needed for ecosystems to function well. Dry regions often suffer from physical water scarcity. Human influence on climate has intensified water scarcity in areas where it was already a problem. It also occurs where water seems abundant but where resources are over-committed. One example is overdevelopment of hydraulic infrastructure. This can be for irrigation or energy generation. There are several symptoms of physical water scarcity. They include severe environmental degradation, declining groundwater and water allocations favouring some groups over others.Water is scarce in densely populated arid areas. These are projected to have less than 1000 cubic meters available per capita per year. Examples are Central and West Asia, and North Africa). A study in 2007 found that more than 1.2 billion people live in areas of physical water scarcity. This water scarcity relates to water available for food production, rather than for drinking water which is a much smaller amount.
Some academics propose a separate type of water scarcity termed ecological water scarcity though some publications argue that this falls within the definition of physical water scarcity. It would focus on the water demand of ecosystems, referring to the minimum quantity and quality of water discharge needed to maintain sustainable and functional ecosystems. Results from a modelling study in 2022 show that northern China suffered more severe ecological water scarcity than southern China. The driving factor of ecological water scarcity in most provinces was water pollution rather than human water use.
Economic water scarcity
Economic water scarcity is due to a lack of investment in infrastructure or technology to draw water from rivers, aquifers, or other water sources. It also reflects insufficient human capacity to meet the demand for water. It causes people without reliable water access to travel long distances to fetch water for household and agricultural uses. Such water is often unclean.The United Nations Development Programme says economic water scarcity is the most common cause of water scarcity. This is because most countries or regions have enough water to meet household, industrial, agricultural, and environmental needs. But they lack the means to provide it in an accessible manner. Around a fifth of the world's population currently live in regions affected by physical water scarcity.
A quarter of the world's population is affected by economic water scarcity. It is a feature of much of Sub-Saharan Africa. So better water infrastructure there could help to reduce poverty. Investing in water retention and irrigation infrastructure would help increase food production. This is especially the case for developing countries that rely on low-yield agriculture. Providing water that is adequate for consumption would also benefit public health. This is not only a question of new infrastructure. Economic and political intervention are necessary to tackle poverty and social inequality. The lack of funding means there is a need for planning.
The emphasis is usually on improving water sources for drinking and domestic purposes. But more water is used for purposes such as bathing, laundry, livestock and cleaning than drinking and cooking. This suggests that too much emphasis on drinking water addresses only part of the problem. So it can limit the range of solutions available.
Challenges
Simple indicators
There are several indicators for measuring water scarcity. One is the water use to availability ratio. This is also known as the criticality ratio. Another is the IWMI Indicator. This measures physical and economic water scarcity. Another is the water poverty index."Water stress" is a criterion to measure water scarcity. Experts use it in the context of Sustainable Development Goal 6. A report by the FAO in 2018 provided a definition of water stress. It described it as "the ratio between total freshwater withdrawn by all major sectors and total renewable freshwater resources, after taking into account environmental flow requirements ". This means that the value for TFWW is divided by the difference between TRWR minus EFR. Environmental flows are water flows required to sustain freshwater and estuarine ecosystems. A previous definition in Millennium Development Goal 7, target 7.A, was simply the proportion of total water resources used, without taking EFR into consideration. This definition sets out several categories for water stress. Below 10% is low stress; 10-20% is low-to-medium; 20-40% medium-to-high; 40-80% high; above 80% very high.
Indicators are used to measure the extent of water scarcity. One way to measure water scarcity is to calculate the amount of water resources available per person each year. One example is the "Falkenmark Water Stress Indicator". This was developed by Malin Falkenmark. This indicator says a country or region experiences "water stress" when annual water supplies drop below 1,700 cubic meters per person per year. Levels between 1,700 and 1,000 cubic meters will lead to periodic or limited water shortages. When water supplies drop below 1,000 cubic meters per person per year the country faces "water scarcity". However, the Falkenmark Water Stress Indicator does not help to explain the true nature of water scarcity.