Transboundary Water Conflicts and Water Transfers

Transboundary waters are rivers, lakes and aquifers shared by two or more countries, and water transfers are engineering schemes that move water from one basin or region to another; both can cause conflict but can also be managed through cooperation and treaties. In brief: more than 260 river and lake basins cross national borders, and over 150 countries share them, so upstream actions such as dams, diversions and pollution affect downstream neighbors. Water-sharing disputes, such as over the Nile, the Indus, the Tigris-Euphrates and the Mekong, are usually settled by negotiation, and cooperation is more common than war. Transfers, such as China’s South-North project, can relieve scarcity but have high financial, social and environmental costs.

Water does not respect political borders, so how it is shared is a central issue of regional stability and development. This guide explains why transboundary conflicts arise, the main case studies, how treaties and institutions work, the benefits and costs of water transfers, compares major cases in a table, works through calculations, outlines the history and corrects common mistakes.

Why do transboundary conflicts arise?

Water is essential, has no substitute and flows from upstream to downstream, so one country’s use affects another’s. Common causes of tension are dams and diversions upstream that reduce or change the timing of flow, irrigation and population growth that raise demand, pollution from upstream users, climate variability that makes droughts more severe, and historical agreements that do not reflect present needs. The risk of conflict is greatest where there are no treaties or institutions, where one country is much stronger than the others and where the basin is already under stress. Studies of the past decades show that most transboundary water interactions are cooperative and that outright “water wars” are rare, though disputes can add to wider tensions.

What are the main case studies?

• The Nile: shared by 11 countries. Under the 1959 agreement between Egypt and Sudan, Egypt receives 55.5 billion m³ a year and Sudan 18.5 billion, out of about 84 billion. Ethiopia, source of most of the Blue Nile’s flow, was not a party, and began building the Grand Ethiopian Renaissance Dam in 2011. It started filling the reservoir in 2020, and negotiations with Egypt and Sudan over the filling and operation continue.
• The Indus: the 1960 Indus Waters Treaty, mediated by the World Bank, assigned the three eastern rivers to India and the three western rivers to Pakistan. It survived wars between the two countries, but has come under strain.
• The Tigris-Euphrates: Türkiye’s large dams, including the Atatürk Dam, in the upstream area, reduce the flow to Syria and Iraq, which are also affected by drought.
• The Mekong: dams in China and in the lower basin affect fisheries, sediments and flows in Cambodia and Vietnam, and the Mekong River Commission was set up in 1995.
• The Jordan basin and the Colorado River: the Jordan is shared by Israel, Jordan, Syria, Lebanon and the Palestinians, and is strongly depleted. The Colorado is over-allocated between seven US states and Mexico, and the Colorado River Compact of 1922 assumed flows higher than later averages.
• Aquifers: there are also hundreds of transboundary aquifers, such as the Nubian Sandstone Aquifer, shared by Egypt, Libya, Sudan and Chad, which are less well governed.

How can countries cooperate?

International law has developed principles of “equitable and reasonable utilization” and “no significant harm” (reflected in the 1997 UN Watercourses Convention, which entered into force in 2014) and obligations to notify neighbors of planned projects. Tools of cooperation include river basin organizations (such as the International Commission for the Protection of the Rhine and the Mekong River Commission), treaties that fix shares or rules, data sharing, joint monitoring, benefit-sharing (sharing the benefits of hydropower or flood control, instead of dividing the water) and mediation by third parties. Cooperation works best when it covers the whole basin and includes groundwater, water quality and the environment.

What are water transfers?

An inter-basin water transfer moves water by canals, tunnels or pipelines from a basin with a surplus to one with a deficit. Well-known examples are:

• China’s South-North Water Transfer Project: moving water from the Yangtze basin to the dry north, including Beijing. The central route opened in 2014 and runs about 1,200 km. It has displaced hundreds of thousands of people.
• California’s State Water Project and the Central Valley Project: transport water from the north to farms and cities in the south.
• Libya’s Great Man-Made River: pipelines that carry fossil groundwater from the Sahara to coastal cities.
• The Lesotho Highlands Water Project: supplies water and hydropower to South Africa.
• The Aral Sea case: the diversion of the Amu Darya and Syr Darya rivers in the Soviet era for cotton irrigation caused the Aral Sea to lose most of its area and volume, leaving a salty desert and ruining fishing communities. It is often cited as a warning about the environmental effects of large diversions.

Benefits include drinking water and irrigation for dry regions and sometimes hydropower. Costs include construction and energy costs, loss of land and homes under reservoirs, damage to donor and recipient ecosystems (reduced flows, spread of species and salinity), conflict between regions and the risk of encouraging wasteful use instead of efficiency.

Major cases compared

Worked example: shares, energy and costs

The values are approximate or hypothetical and illustrate calculations.

1. Treaty shares: out of about 84 billion m³ of annual Nile flow measured at the Aswan High Dam, the 1959 agreement allocated 55.5 to Egypt and 18.5 to Sudan, a total of 74 billion. The remaining 84 − 74 = 10 billion m³ were assumed lost to evaporation. Egypt’s share is 55.5 ÷ 84 = 66%, and Sudan’s is 18.5 ÷ 84 = 22%.
2. Filling a reservoir: a dam reservoir holds 74 billion m³. If the river flow is 49 billion m³ a year and half is kept for the reservoir each year, it takes 74 ÷ (0.5 × 49) = about 3 years to fill, but the downstream flow is cut by 24.5 billion m³ a year, half of the river, during the filling.
3. Energy to lift water: the energy to lift 1 m³ (1,000 kg) by 100 m is E = m × g × h = 1,000 × 9.81 × 100 = 981,000 J, which is 981,000 ÷ 3,600,000 = 0.27 kWh. With a pump efficiency of 80%, it is 0.27 ÷ 0.8 = 0.34 kWh per m³.
4. Pumping cost: a transfer of 1,000,000,000 m³ a year lifted by 100 m needs 1,000,000,000 × 0.34 = 340,000,000 kWh, which at 0.08 per kWh costs 27,200,000 a year.
5. Transfer volume: a canal with a flow of 300 m³/s carries 300 × 31,536,000 = 9,460,800,000 m³ a year, about 9.5 billion.
6. Cost per cubic meter: a project that costs 20 billion to build, and moves 9.5 billion m³ a year for 50 years, delivers 475 billion m³ in total, so the construction cost is 20,000,000,000 ÷ 475,000,000,000 = 0.042 per m³, before operating and environmental costs.

How have water treaties and transfers developed?

Agreements over water go back thousands of years: a treaty between the Mesopotamian city-states of Lagash and Umma around 2500 BCE is often cited as the earliest known. In the 20th century, treaties such as the Colorado River Compact (1922), the Nile agreements (1929 and 1959) and the Indus Waters Treaty (1960) divided water among users. The Helsinki Rules (1966) and the UN Watercourses Convention (1997) set out principles. Large transfers were built from the Roman aqueducts to the 20th-century canals in California and the former Soviet Union, and in the 21st century, China’s South-North project is the largest. Today, climate change, population growth and dams raise new tensions, and many experts urge integrated basin management and benefit sharing.

Which mistakes are common?

Mistake 1: Predicting “water wars” as the usual result

History shows that countries sharing water usually cooperate, and the shared need often brings negotiation. Tensions are real, but they rarely lead to war.

Mistake 2: Thinking that upstream countries always hold all the power

Downstream countries may have military, economic or historical advantages, and cooperation often depends on benefits for both sides.

Mistake 3: Believing that transfers create water

Transfers only move water. They shift scarcity and can harm the donor region and the environment.

Mistake 4: Ignoring groundwater

Shared aquifers are rarely covered by treaties, though they are heavily used and are often a main source of drinking water.