Two forms of water scarcity

Water scarcity occurs when the amount of water available in a place cannot meet demand. The shortage may involve the total supply, people’s ability to access that supply, or both.

Physical water scarcity occurs when water consumption approaches or exceeds the renewable supply. Although common in dry climates, it can also develop when rivers, lakes and aquifers are persistently overdrawn.

Economic water scarcity occurs when water is available, yet people cannot obtain enough safe water because of inadequate investment, infrastructure, institutions or household incomes. The problem is unequal access, rather than an absolute physical shortage.

Scarcity changes across space and over time. It depends on climate, seasonality, population density, agricultural and industrial demand, storage capacity, water-transfer systems, infrastructure and the power of different users to secure access. During a shortage, a wealthy city may continue to receive water while nearby rural or low-income communities face restrictions.

Drought: causes and development

Drought is an extended period when water availability falls substantially below the normal level for a place. What counts as “normal” varies between climates, so drought has a relative threshold rather than a universal one.

A drought may develop through a connected sequence:

1. Persistent changes in atmospheric circulation reduce precipitation.
2. High temperatures increase evaporation and plant water loss.
3. Soil moisture declines, placing crops and natural vegetation under stress.
4. River discharge, reservoir storage and groundwater recharge decrease.
5. Continued abstraction lengthens the shortage or makes it more severe.

Human activity can make a climatic drought worse. Deforestation and soil degradation reduce infiltration. At the same time, intensive irrigation, urban demand and over-abstraction can rapidly deplete stored water. When infrastructure is limited and management is weak, reduced rainfall may develop into a serious human crisis.

Impacts of drought

Environmental impacts include vegetation stress, loss of wetland habitat, reduced river flow, falling lake levels, soil erosion and a greater risk of wildfire. Lower flows dilute pollutants less effectively, so drought may reduce water quality as well as water quantity.

Crop failure, livestock losses, reduced hydroelectric output, disrupted industry and higher food and water prices are economic impacts. Social effects may include food insecurity, poor sanitation, illness, migration and conflict between domestic, agricultural, industrial and environmental users. The impacts aren’t evenly distributed: richer households, firms and governments usually have more capacity to store, purchase or transfer water.

Water quantity and water quality

Water quantity is the volume of water available to users and ecosystems. Precipitation, storage, river discharge, recharge, abstraction and consumption all affect it.

Water quality describes water’s physical, chemical and biological condition, along with its suitability for a particular use. Water may be abundant but unsafe if it contains pathogens, nutrients, salts or other pollutants. Alternatively, clean water may be available in quantities too small to meet demand.

Quantity and quality affect each other. When river discharge falls, pollutant concentrations rise. Contamination also removes some of the existing supply from safe use, creating effective scarcity.

Agriculture and water quality

Agriculture can cause non-point-source pollution when contaminants wash off many fields instead of leaving through a single identifiable pipe. Runoff from rainfall and irrigation carries soil, fertilizers, animal waste and dissolved salts into rivers, lakes and groundwater.

How severe the pollution becomes depends on fertilizer application, livestock density, irrigation methods, soil drainage, slope, precipitation and the distance from farmland to water bodies. The effects may be felt far downstream from the agricultural activity that caused them.

Eutrophication

Eutrophication occurs when nutrients enrich a water body, causing excessive growth of algae and other aquatic plants. Agricultural fertilizers and animal waste supply large amounts of nitrates and phosphates.

The process develops as follows:

1. Nutrient-rich runoff enters a river, lake or coastal water body.
2. Algae grow rapidly and form an algal bloom, blocking sunlight.
3. With less photosynthesis, submerged plants die.
4. Bacteria decompose the dead organic material.
5. As the bacteria respire, they consume dissolved oxygen.
6. The oxygen-poor water kills fish and reduces aquatic biodiversity.

Some blooms also produce toxins. This further limits the use of water for recreation, fishing or domestic supply.

Irrigation and salinization

Salinization is the build-up of soluble salts in soil or water. It is particularly likely in dry regions, where evaporation is high and effective drainage does not remove irrigation water.

Irrigation water naturally contains small quantities of dissolved salts. The water evaporates or crops take it up, leaving the salts behind in the soil. With repeated irrigation, their concentration rises. Too much irrigation may also raise the water table, which allows saline groundwater to move upward through the soil by capillary action. Crop yields then fall because plant roots find it increasingly difficult to absorb water.

Carefully controlled irrigation and improved drainage can flush salts below the root zone. However, the resulting saline drainage water may pollute rivers or downstream farmland. Managing salinization can therefore shift costs from one place or stakeholder to another.

Stakeholders and unequal power

A stakeholder is a person, group or organization with an interest in, or influence over, a water-management issue. Relevant stakeholders include:

• farmers and agricultural businesses seeking reliable production;
• downstream residents needing safe water;
• fishing and tourism businesses affected by degraded ecosystems;
• government regulators and water agencies;
• environmental organizations and scientists;
• Indigenous or local communities with cultural and livelihood connections to water.

These actors don't have equal power. Large agricultural businesses may be able to influence policy or pay for treatment technology, while small farmers and downstream communities may have less control over decisions. Governments can regulate fertilizer use, charge for irrigation water, improve drainage, monitor pollution or pay farmers to adopt less damaging practices. Because pollution crosses farm and administrative boundaries, effective action usually requires cooperation throughout the drainage basin.

Illustrative detailed examples

The Chesapeake Bay in the United States provides an example of eutrophication. Fertilizer and animal-waste runoff from a large drainage basin can contribute to algal growth and oxygen-depleted water. Farmers, state authorities, environmental organizations, fishing communities and urban residents have different priorities. Basin-wide controls rely on cooperation across several jurisdictions.

The Murray–Darling Basin in Australia provides an example of salinization and the tensions between irrigated agriculture and downstream water quality. Irrigators, basin authorities, environmental groups, Indigenous communities and downstream settlements disagree over water allocations, drainage and the costs of reducing salt loads.

These examples are illustrative; the class may use different detailed examples. Any examples selected must identify the agricultural process, trace its environmental consequences and explain the roles and relative power of different stakeholders.

Lakes as pressured water stores

Lakes supply water to households, farms, industry and ecosystems. Yet they’re vulnerable: changes elsewhere in the drainage basin affect both the quantity and quality of water that reaches them.

As economies grow, industrial production, electricity generation, commercial agriculture, tourism and household consumption all increase water demand. Abstraction from the lake, or diversion of the rivers that feed it, can cause water levels to fall. Meanwhile, sewage, industrial waste, sediment and nutrient-rich agricultural runoff can damage water quality.

This creates two connected pressures. Less water enters or remains in the lake, and pollutants or salts become more concentrated in the water left behind. Lower lake levels may destroy shoreline wetlands, reduce fish habitat, disrupt transport and expose contaminated lake beds.

Aquifers and groundwater pressure

An aquifer is a body of permeable rock or sediment that stores and transmits groundwater. Water replenishes aquifers by infiltrating the ground and moving downward through permeable material. This process is recharge.

If pumping exceeds recharge, the groundwater table falls. Wells may dry up, the cost of pumping rises and groundwater-fed rivers or wetlands receive less water. In coastal areas, excessive pumping can draw salt water into an aquifer. Some aquifers recharge so slowly that intensive abstraction effectively mines a finite store.

Groundwater quality can deteriorate too. Fertilizers, pesticides, sewage and industrial pollutants may infiltrate through the soil. Cleaning contaminated groundwater is difficult and expensive because the water moves slowly and remains hidden below the surface.

Economic growth and population migration

Economic growth brings greater water demand and more pollution. Expanding cities need larger municipal supplies, while new factories, irrigated farms and energy projects compete for water from the same lakes and aquifers. Governments may support extraction because it generates income and employment, even when withdrawals are unsustainable in the long term.

Population migration shifts the concentration of demand. Rural-to-urban migration enlarges cities, sometimes faster than water-supply and sewage infrastructure can be built. Movement into dry regions, tourist areas or commercial farming zones can place extra pressure on aquifers that replenish slowly. Displaced populations may also settle in places where access to safe water is already limited.

These effects are connected across space. Pumping in one district may lower the water table beneath neighbouring communities. Upstream pollution or river diversion can affect a lake far downstream. As a result, the stakeholders who receive the economic benefits aren’t always those who bear the environmental and social costs.

Management and power

Water agencies can use abstraction permits, metering, pricing, pollution controls and land-use regulation. Their success, however, depends on enforcement and political power. Large cities, industries and commercial farms may gain access to deep wells or public infrastructure. As water levels fall, small farmers, poorer households and ecosystems may lose access.

Management needs to address the connected water system as a whole, rather than dealing with each well, river or lake in isolation. For use to remain sustainable, withdrawals must reflect recharge and inflow. Pollution also needs to be controlled across the contributing drainage basin or recharge zone.

Why shared water can generate conflict

An internationally shared water resource is a river, lake or aquifer that crosses national borders or is used by more than one country. A decision in one state may change the quantity, timing or quality of water available elsewhere.

Conflict is more likely when:

• an upstream state controls flow through dams, diversion or abstraction;
• downstream states rely heavily on the resource;
• population growth and economic development push up demand;
• drought or variable rainfall cuts supply;
• irrigation, hydropower, domestic supply and ecosystem protection compete for water;
• pollution crosses an international boundary;
• borders, dam projects or water allocations are politically disputed;
• institutions for sharing information and resolving disputes remain weak.

Location shapes the balance of power. Upstream states can often change river flows directly. Downstream states, however, may have greater economic, diplomatic or military influence. Power comes from geography as well as wider political relationships.

Conflict doesn’t have to involve armed violence. Diplomatic tension, delayed projects, protests and legal disputes are all forms of conflict. It may also involve threats to revise agreements or disagreements over scientific evidence.

Stakeholders and routes towards resolution

Stakeholders can include national governments, regional authorities, dam operators and farmers. Electricity users, local and Indigenous communities, environmental organizations and international institutions may also be involved. Their priorities often clash: one actor may favour hydropower, while another relies on seasonal flows for irrigation, fisheries or wetlands.

Attempts to resolve conflict may involve:

• treaties that set out rights and responsibilities;
• agreed water allocations or rules for operating dams;
• joint river-basin commissions;
• shared monitoring and the exchange of flow data;
• notification and consultation before new projects begin;
• mediation, arbitration or legal settlement;
• benefit sharing, such as exchanging water regulation for energy or investment.

For an agreement to last, it must respond to changing demand and variable supply. It also requires monitoring, finance and enforcement. Affected communities need to participate, rather than leaving decisions only to national governments.

Illustrative case study: the Indus river system

India and Pakistan are the principal users of the Indus river system. Pakistan depends strongly on its waters for irrigated agriculture. India lies upstream on important tributaries, so its dam construction and river management can cause downstream concern about the timing and reliability of flows. Wider political distrust makes these disagreements more intense.

The Indus Waters Treaty created a framework that divided use of the eastern and western rivers between the two states. India retained primary use of the eastern rivers. Pakistan received primary use of the western rivers, subject to specified upstream uses by India. The treaty reduced uncertainty over allocation, but it did not remove every disagreement.

The two national governments remain the main actors. The Permanent Indus Commission provides a formal route for raising technical concerns, but regular communication has been disrupted since India announced the treaty’s suspension in April 2025. The World Bank helped facilitate the original agreement and has a limited procedural role when disputes move beyond bilateral discussion. Particular technical and legal disagreements may be referred to neutral experts or arbitration.

Farmers and communities in Pakistan want reliable irrigation flows. Indian authorities and electricity users, meanwhile, may support upstream hydropower development. Environmental needs and locally affected communities can have less influence than national priorities. Disputes continue over dam design, data and treaty interpretation, showing that an agreement may manage conflict without fully resolving its political causes.

This is an illustrative case study; the class may use another internationally shared resource. A complete case study must establish the geography of the resource, explain why conflict developed, identify stakeholders and assess how they attempted to reach a resolution.