Archive for the ‘Tribunal Decision’ Category

U.S. Supreme Court Issues Decision in First Ever Dispute Over Interstate Groundwater – Implications for International Law

Monday, December 13th, 2021

This essay is written by Gabriel Eckstein, Professor of Law at Texas A&M University, director of the TAMU Law Program in Energy, Environmental, and Natural Resources Systems, and director of the International Water Law Project. He can be reached at gabrieleckstein [at] (This essay was republished in Global Water Forum, Dec. 21, 2021, available at

On 22nd November 2021, in the case of Mississippi v. Tennessee, the Supreme Court of the United States issued its first ever decision in a dispute between two U.S. states over a transboundary aquifer.  The Justices’ decision was unanimous with the Court dismissing Mississippi’s case and holding that “the waters contained in the Middle Claiborne Aquifer are subject to equitable apportionment,” and that U.S. states may not “exercise exclusive ownership or control” over interstate waters flowing within their borders.  While the case involved an entirely domestic U.S. dispute, it is nonetheless an interstate dispute over cross-border groundwater resources. Thus, it could have a significant jurisprudential impact on the development of international law for transboundary groundwater resources.


The Middle Claiborne Aquifer. From U.S. Geological Service.

The Middle Claiborne Aquifer (also known as the Memphis Sand Aquifer) is a relatively large groundwater-bearing formation that underlies eight states in the United States, including Mississippi and Tennessee.  Decades ago, Tennessee installed groundwater wells on its side of the border to supply the growing city of Memphis. More recently, Tennessee installed additional wells close to its border with Mississippi to supply Memphis and the surrounding communities.  Memphis, with a population of 1.15M people, is one of the largest cities in the United States that relies exclusively on groundwater for its municipal water supply utilizing around 160 wells.  In contrast, Mississippi has withdrawn comparatively very little groundwater from the aquifer on its side of the border.  Most of the extractions in Mississippi supply individual households and some agricultural activities.

In 2014, Mississippi sued Tennessee and the City of Memphis claiming that since 1985, Memphis had stolen 252 billion gallons (954 million m3) of Mississippi’s groundwater.  While Tennessee’s wells were drilled vertically and did not extend across the border, Mississippi asserted that the cones of depression of Tennessee’s wells crossed into Mississippi and diverted that state’s groundwater into Tennessee.  Mississippi also claimed that it had an ownership interest in that stolen groundwater and demanded compensation in the amount of USD $615 million.  In response, Tennessee asserted that transboundary groundwater resources in the United States should be subject to the same doctrine as transboundary surface waters, namely, the doctrine of equitable apportionment.  Hence, it asked the Court to dismiss Mississippi’s case since Mississippi had not filed a claim based on that doctrine.  Mississippi responded that equitable apportionment should not apply in its case because groundwater and surface waters have different properties and characteristics, and because Tennessee had already withdrawn 252B gallons of groundwater before there was a chance to divide it in a fair manner.

The Decision

In surprisingly quick action, less than two months following oral arguments, the Supreme Court issued its decision.  The Court outrightly rejected all of Mississippi’s exclusive ownership claims and ruled that “the waters contained in the Middle Claiborne Aquifer are subject to equitable apportionment.”

NW-SE hydrostratigraphic cross section beneath the city of Memphis and the adjacent states of Arkansas (AR) and Mississippi (MS). From Michael Campana, Mississippi v. Memphis: The Curious Case of the Memphis Sand Aquifer, in Transboundary Groundwater Resources: Sustainable Management and Conflict Resolution (Fried and Ganoulis, Eds. 2016, Lambert Academic Publishing).

In adjudicating the case, the Court acknowledged that the Court has “never considered whether equitable apportionment applies to interstate aquifers.” However, it quickly asserted that, for three reasons, equitable apportionment of the Middle Claiborne Aquifer would be “‘sufficiently similar’ to past applications of the doctrine to warrant the same treatment.”  First, it stated that while the Court had only applied equitable apportionment to transboundary resources, the “Middle Claiborne Aquifer’s ‘multistate character’ seems beyond dispute.”  Second, it explained that the aquifer “contains water that flows naturally between the States” and that its distinct characteristics, including the considerably slower movement of groundwater in comparison to surface flows, are irrelevant to the analysis.  Lastly, the Court said that where one state’s use of a transboundary resource affects the other state (here, Tennessee’s pumping of the groundwater affected the aquifer in Mississippi through the cone of depression, which extended underneath Mississippi), indeed, “[s]uch interstate effects are a hallmark of our equitable apportionment cases.”  Accordingly, the Court concluded that “the judicial remedy of equitable apportionment” applies to the waters of the Middle Claiborne Aquifer.

In addition, the Court thoroughly rejected Mississippi’s claim to sovereign ownership of the groundwater in the portion of the formation that was located within its borders.  The Court recognized that each state “has full jurisdiction over the lands within its borders, including the beds of streams and other waters.”  However, it asserted that “such jurisdiction does not confer unfettered ‘ownership or control’ of flowing interstate waters themselves.”

Implications for International Law

While nation’s domestic court decisions are not regarded as primary sources for international law, decisions from federal jurisdictions often have been influential in its development.  This is especially true in the advancement and evolution of international water law where the jurisprudence of the U.S. Supreme Court in interstate water disputes has featured quite prominently.  Thus, it is likely that the recent decision could prove significant in two regards.

Equitable and reasonable utilization

Equitable and reasonable utilization is considered as one of the keystone principle of international water law.  However, as Professor Rhett Larson explains, its origin can be traced back largely to U.S. Supreme Court jurisprudence and that Court’s doctrine of equitable apportionment.  For example, both equitable apportionment and equitable and reasonable utilization focus on the notion of equality of states under law, and both advocate equity in the allocation of benefits derived from transboundary waters.  Moreover, the factors established by the U.S. Supreme Court for determining equitable apportionment are very similar to those laid out in Article 6 of the Watercourses Convention for determining equitable utilization.  For example, while the U.S. doctrine considers “physical and climatic conditions” when evaluating the equities, international law ponders the “[g]eographic, hydrographic, hydrological, climatic, ecological and other factors of a natural character.”  Although there are also important differences between the two doctrines, it suffices to say that U.S. Supreme Court decisions in interstate U.S. water disputes have greatly influenced the development of the international law principle of equitable and reasonable utilization.

Application of that doctrine to international transboundary groundwater resources, however, is not entirely novel.  While far from being widely accepted, the concept, or something close to it, does appear in a few international instruments governing specific transboundary aquifers: the 2010 Guarani Aquifer Agreement ratified by Argentina, Brazil, Paraguay, and Uruguay; the 2013 Regional Strategic Action Programme for the Nubian Aquifer System adopted by Chad, Egypt, Libya, and Sudan; and the Memorandum of Understanding for the Establishment of a Consultation Mechanism for the Integrated Management of the Water Resources of the Iullemeden, Taoudeni/Tanezrouft Aquifer System, which has yet to come into force for the signatory states of Algeria, Benin, Burkina Faso, Mali, Mauritania, Niger, and Nigeria.

Understandably, three instruments employed for three different transboundary aquifers does not establish the existence of a customary international norm.  However, now that the U.S. high court has ruled that waters flowing through the aquifer underlying the Mississippi-Tennessee border are subject to equitable apportionment, other nations may be more inclined to explore the relevance of the comparable international law version of the doctrine—equitable and reasonable utilization—to groundwater resources shared with their neighbors.


In the U.S. Supreme Court case, Mississippi argued that it had an absolute “ownership” right to all groundwater beneath its surface.  As a result, it sought USD $615 million in compensation from Tennessee for groundwater that the latter state caused to flow from underneath Mississippi and to Tennessee’s pumps.  In rejecting this claim, the U.S. Supreme Court recognized that while each U.S. state has “full jurisdiction” over “the lands within its borders, including the beds of streams and other waters,” it may not “exercise exclusive ownership or control” of interstate waters flowing within its territory.  Otherwise, the Court asserted, it would allow an upstream (or up-aquifer) State “to completely cut off flow to a downstream one, a result contrary to our equitable apportionment jurisprudence.”  Thus, U.S. states may not claim sovereign ownership of the groundwater flowing beneath their territories.

Model of a transboundary aquifer. From S. Puri, G. Arnold Challenges to management of transboundary aquifers: The ISARM Programme: 2nd International Conference, Sustainable Management of transboundary waters in Europe, Miedzyzdroje, April 2002 (2002)

The Court’s decision is also noteworthy for the language it used.  In recognizing a state’s limited rights to the portion of cross-border land and resources located within its borders, and specifically to “the beds of streams and other waters,” the Court acknowledged only the right to “full jurisdiction,” but not to sovereignty.  This could be a critical distinction as “full jurisdiction” suggests a right to control or administer, but does not accord the full right of ownership that would ensue from sovereignty.  Moreover, by emphasizing “the beds of streams and other waters,” the Court seemed to focus on the container holding the water.  Thus, the Court’s decision could be interpreted as a right to control, regulate, and manage a portion of a transboundary aquifer—the matrix containing the groundwater—found within a country’s boundaries, but not an outright entitlement to claim ownership of that formation segment.  While the distinction may seem semantical, full jurisdiction could prove to be a more constrained right as compared to sovereignty in relation to other established interstate obligations, such as cooperation, the peaceful resolution of disputes, and equitable apportionment when arguing before the U.S. Supreme Court.

In the context of international law for transboundary groundwater resources, the notion of sovereignty has been controversial.  While sovereignty was excluded from the UN Watercourses Convention, it did find its way into Article 3 of the Draft Articles on the Law of Transboundary Aquifers (despite fervent objections—see here) where each aquifer state is accorded “sovereignty over the portion of a transboundary aquifer or aquifer system located within its territory.”  This formulation was justified by some on grounds that groundwater was akin to other natural resources (like oil, gas, and other minerals) that were subject to ownership claims articulated in the UNGA Resolution 1803 (XVII) of 14 December 1962 on Permanent Sovereignty Over Natural Resources; others argued that sovereignty necessarily applies to the stationary, groundwater-bearing, rock formation located within each country, albeit maybe not the groundwater itself.  To many water law experts, the provision was anathema to more recent understanding of international water law, especially in light of emerging principles of international environmental law.  Professor Stephen McCaffrey, one of the ILC Special Rapporteurs for what became the UN Watercourses Convention, asserted that “In this one provision, the ILC has managed to reverse over 100 years of development of international-watercourse law,” and suggested that the provision harkened back to the now discredited Harmon Doctrine.

The U.S. Supreme Court’s pronouncement in Mississippi v. Tennessee marks a significant departure from the formulation found in the Draft Articles.  By asserting that a state may not seek to control exclusively interstate waters flowing within its territory, including groundwater, the Court mandated that interstate waters were common to all riparians and could be utilized and managed only with due regard given to the rights of other riparian states.  Potentially more significant, by focusing on the matrix containing the groundwater and using the “full jurisdiction” language, the Court may have signaled its disfavor of unrestrained sovereignty over groundwater-bearing formations that cross political boundaries, and its preference for cooperation and a collaborative approach to the management of transboundary aquifers.  In the international water law context, this equates with the notion of limited territorial sovereignty that now prevails for international watercourses, and possibly even the more progressive community of interest theory (see here).  Thus, the Court’s decision squarely sides with those who fought against inclusion of the sovereignty provision in the Draft Articles (see here).


Until now, there has never been a national judicial body (in the United States or elsewhere) that has considered a case between two political jurisdictions fighting over the right to use the waters of a transboundary aquifer.  As a result, the allocation of, rights to, and sovereignty in transboundary groundwaters and aquifers have been uncertain under both U.S. domestic law and international law.  While the case takes a great leap forward in clarifying the law within the United States, it may also prove to be influential in the international arena and serve as basis for the ongoing development of international law for transboundary groundwater resources.

The Kishenganga Awards and their Contributions to International Water Law

Wednesday, August 5th, 2015

The following post is by Dr. Mara Tignino, Senior Lecturer and Coordinator of the Platform for International Water Law, Faculty of Law, University of Geneva. She can be reached at Mara.Tignino [at]


In May 2010, Pakistan initiated an arbitration proceeding against India concerning the construction of a hydroelectric infrastructure project (“KHEP”) undertaken by India on the Kishenganga River—part of the Indus River basin. The KHEP is situated in India-administered Jammu and Kashmir in north-west India, about 12 kilometres upstream of the Line of Control with Pakistan-administered Jammu and Kashmir, and is aimed at producing hydropower via a diversion of the River’s flow. Once completed, the diverted waters would flow through a tunnel around 23.5 kilometres long toward a power facility situated 666 meters below the Kishenganga dam. The water will then be redirected into Wular Lake and the River Jhelum, which flows into the territory of Pakistan. The falling water would drive turbines producing about 330 megawatts of electricity. According to Pakistan, the KHEP will have an impact on water flow downstream in Pakistan and affect its own production of hydropower.

Kishenganga Hydroelectric Project (Source: Partial Award, p.51)

Kishenganga Hydroelectric Project (Source: Partial Award, p.51)

The uses of the Indus River and its tributaries are regulated by the Indus Waters Treaty, adopted by India, Pakistan and the International Bank for Reconstruction and Development (IBRD) in 1960. Article IX of the treaty provides for the establishment of mechanisms for the settlement of differences and disputes between the two States. As a result of Pakistan’s request, an arbitral tribunal composed of seven arbiters was established under article IX, which subsequently issued four decisions: an Order on Interim Measures in September 2011, based on an application made by Pakistan in June 2011, a Partial Award in February 2013, a Decision on India’s Request for Clarification or Interpretation in May 2013, and a Final Award, issued in December 2013. All four decisions were adopted unanimously.

Signed after ten years of negotiations, the Indus Waters Treaty represented an ambitious landmark in the development of international water law. The treaty is emblematic of the potential for international law to facilitate cooperation in the governance of international watercourses. As emphasized by the tribunal itself, the treaty has been continuously applied for over 50 years, despite recurring hostilities in the Kashmir region, including three episodes of direct armed conflict between India and Pakistan. In fact, while Pakistan had made use of the dispute settlement procedures of the treaty once before—in 2006, it requested the intervention of a Neutral Expert under article IX in the case of the Baglihar hydropower project—this was the first time that an arbitral tribunal had been established to settle a dispute concerning the application and the interpretation of the treaty.

Much as the treaty itself contributed to the development of substantive law on international watercourses, both the process and outcome of the arbitration offered noteworthy innovations in the settlement of disputes on transboundary water resources:

  1. In procedural terms, the inclusion of an engineer among the members of the tribunal offered an interesting approach to balancing the needs for various forms of expertise in the determination of the issues (the Neutral Expert charged with resolution of the 2007 Baglihar dispute was also an engineer). The presence of technical experts as equal participants in dispute settlement mechanisms facilitates the understanding of complex factual issues related to the construction and exploitation of hydropower infrastructures.
  2. From the perspective of substantial international environmental law, the recognition in the award of an obligation to ensure a minimum environmental flow in an international watercourse offers a possible indicator of future developments. The tribunal held that India could divert waters from the Kishenganga River, but that it had to ensure a continuing minimum flow rate of 9 cubic meters of water per second in the River itself (Final Award, p.326). Parties must provide the Permanent Indus Commission with daily data on River flows and the information on the inputs and withdrawals of water from the reservoir. According to the arbiters, the Commission is the most appropriate mechanism to ensure the exchange of data and monitoring of the uses of the tributaries of the Indus River (Final Award, par.121).
  3. Strikingly, the judges rejected the application of the precautionary principle to the case. Pakistan had argued that the flows of the Indus tributaries at the Line of Control are difficult to measure, and the Parties gave different estimations of future minimum flow levels. The tribunal recognized future flows levels would be uncertain, depending both on future uses and on factors outside the control of either India or Pakistan, such as climate change (Final Award, par.117). Rather than basing their judgment on the precautionary principle, they chose to account for this uncertainty by requiring India to finalise the KHEP in a manner that would allow for responsiveness to future variations in flow levels.
  4. Finally, the tribunal offered a lynchpin for the sustainability of this approach by creating a window for reconsideration: if, within seven years after the diversion of the Kishenganga River is finalized, one of the Parties considers it necessary to review the quantity of the minimum environmental flow as decided by the arbitral tribunal, the flow will be submitted to the Permanent Indus Commission or other mechanisms established by the Treaty (Final Award, par.119).

Members of the Court of Arbitration, 20 August 2012 Standing : H.E. Judge Peter Tomka, Judge Bruno Simma, Professor Lucius Caflisch, Professor Jan Paulsson. Seated : Sir Franklin Berman KCMG QC, Judge Stephen M. Schwebel (Chairman), Professor Howard S. Wheater FREng

Members of the Court of Arbitration, 20 August 2012
Standing: H.E. Judge Peter Tomka, Judge Bruno Simma, Professor Lucius Caflisch, Professor Jan Paulsson. Seated: Sir Franklin Berman KCMG QC, Judge Stephen M. Schwebel (Chairman), Professor Howard S. Wheater FREng

The decisions of the arbitral tribunal specify the general obligations related to the construction of hydroelectric projects upstream and downstream of an international watercourse. Thus, the Tribunal affirms that “There is no doubt that States are required under contemporary customary law to take environmental protection into consideration when planning and developing projects that may cause injury to a bordering State” (Partial Award, par.449), and takes note of the principle of sustainable development, the obligation to carry out a transboundary environmental impact assessment and the broader duty to avoid transboundary harm (Partial Award, pars. 448-451). In considering these obligations both in terms of conventional law, according to the Indus Waters Treaty, and in terms of customary law, the arbiters have contributed to the development and clarification of general principles of international water law relating to the environmental protection of transboundary water resources.