Hydrologic Reality: International Water Law and Transboundary Ground-Water Resources

by Gabriel E. Eckstein
Based on the lecture presented at the conference:
"Water: Dispute Prevention and Development"

American University Center for the Global South, Washington, D.C.
October 12 - 13, 1998


This presentation was inspired by a conference I recently attended at which I spoke on ground-water resources and international water law in the context of the International Court of Justice's Danube Dam Case. Although the conference - combined XXVIII-th Congress of the International Association of Hydrogeologists and Annual Meeting of the American Institute of Hydrology - was a scientific gathering of hydrologists, hydrogeologists, engineers, and other scientists from around the world, one of the sessions was dedicated solely to legal issues related to water resources.

At this session, part of my presentation focused on the deficit of scientific bases for international and domestic laws, policies, and regulations governing the environment, as well as the absence of scientific knowledge among legislators, policymakers, and the judiciary. Having made that assertion among scientists, I was not too surprised at the unchallenged acceptance of the proposition. I was, however, quite surprised by the degree of consensus and acknowledgment of the problem within the audience. In fact, the issue seemed to permeate many of the other presentations at this session and appeared to be a constant undercurrent of many of the problems these scientists were facing in their countries.

In the context of water resources and water scarcity, and in particular when dealing with the regulation, management and conservation of such resources, there appears to be a serious misunderstanding within the political and legal communities of the nature of ground-water and surface water and the interrelationship between the two. It is this misunderstanding which lay at the heart of the misgivings of the scientists I spoke with, and which all too often has resulted in policies, laws, and court decisions that are inadequate and ineffective in dealing with modern water problems.

Thus, before I proceed with the legal issues, I will first present some facts and fundamental principles stemming from the nature of the hydrological/hydrogeological system. I think such a discussion is necessary precisely because of the pervasiveness of the misunderstanding. I will then discuss the scope of the recently adopted United Nations Convention on the Law of the Non-Navigational Uses of International Watercourses in the context of what I call "hydrologic reality," along with a number of case examples.

Geology 101: Hydrologic Reality

Global Water Resources

Of the vast amount of water that covers more than two-thirds of the Earth, only a little more than 2.5 percent is freshwater. While that may not sound like very much, what we readily see as surface freshwater, such as is found in lakes, streams, and other surface bodies of water, make up only 0.007 percent of global water reserves and less than 1 percent of the total amount of freshwater. The majority of freshwater - 68.7 percent of global freshwater - is in the form of glaciers and permanent snow, primarily in the polar regions, while slightly more than 30 percent is found in ground-water resources. The following chart provides a more complete picture of global water supply.

Global Water Supply


As a Percent of
All Water

As a Percent of Global Freshwater

Earth's Oceans

97.50 %


Glaciers & Permanent Snow

1.74 %

68.70 %

Fresh Ground-Water

0.76 %

30.10 %

Salt Ground-Water

0.99 %


Ground Ice & Permafrost

0.02 %

0.86 %

Fresh Water Lakes

0.007 %

0.25 %

Salt Water Lakes

0.006 %


Soil Moisture

0.001 %

0.05 %


0.001 %

0.04 %


0.0008 %

0.03 %


0.0002 %

0.006 %


0.0001 %

0.003 %

Compiled from World Resources Institute, Barberis, and Bouwer.

Considering the quantity of global ground-water in relation to surface water, it is safe to say that we have not even come close to running out of freshwater. This is even more evident when considering the fact that at present, about two-thirds of global freshwater use (including for domestic, agricultural, and industrial purposes) comes from surface sources, while only 1/3 comes from ground-water. Hence, questions of water scarcity and management concern not so much the lack of adequate water supplies, but rather the poor distribution of water resources found in nature. This predicament is the result of a long geological history of interaction between the evolving lithosphere with the other components of the global system, notably the hydrosphere, the atmosphere and the biosphere.

The Hydrologic Cycle

The hydrologic cycle is the system in which water, in its various shapes and forms, travels from the atmosphere, to the Earth, and back again in a constant cycle of rebirth. Generally, water falls from the atmosphere in the form of rain, snow, sleet, and so on. That which falls on land, tends to flow over the land, such as in streams, rivers, and lakes, or percolate into the earth to underground aquifers. Moreover, throughout its surface travels and especially once it reaches large bodies of water, such as oceans, water evaporates and returns to the atmosphere where it continues in the cycle.

As gravity is an omnipresent force, water always flows from higher to lower elevations and eventually ends up in the oceans or other low point from which it can no longer flow downward. While flowing downward, though, surface- and ground-waters will not always flow in the same geographical direction. Downward water flow is also dependant on the permeability of soils and strata, as well as on various obstacles that such flow may encounter (i.e., dams, bedrock, low permeability zones, etc.). Thus, it is possible to have a stream flowing down the side of a mountain in one direction, while water in a related underlaying aquifer flowing in another direction following the gradient of porous strata.

While this is merely a simplified description of the hydrologic cycle, suffice it to say that water at its various stages in the cycle, and in its various shapes and forms, is interrelated and un-severable from the cycle. Where a component part of the cycle is impacted in terms of either quality or quantity, or both, it is bound to affect other component parts of the cycle. This is an imperative that must be understood, especially in the context of regulating, managing, and conserving water resources. It is especially evident when looking directly at a surface body of water, such as a stream or a lake, that is related to a subsurface aquifer.

Gaining and Losing Streams

As described earlier, precipitation that falls on the land either flows into streams, rivers and lakes, or seeps into the soil and percolates to the water table and underlaying aquifers. Where the ground-water table is located well below the bottom of a stream or a lake, and where the soil is moderately permeable, water tends to percolate from the surface water body (a stream or a lake) downward, recharging the local ground-water resource (or aquifer). This is called a losing stream or lake. Where, however, the ground water table intersects the stream channel or a lake, the surface water bodies commonly provide drainage to the elevated ground water table, while the ground water tends to flow into that stream or lake. Such a situation is called a gaining stream of lake.

This exchange between surface and subsurface water resources is not unique, and is significant in that conditions affecting the quality and quantity of the water on one side of the relationship may have consequences on interrelated water resources. Moreover, it is very common to have mutual relationships for surface and underground water sources that vary in time and space. A river, for example, may be losing at one point of its course, and gaining at another, or a given stretch of a river may be losing during the Fall season while gaining during Spring.

Water in the Danube River, for example, generally flows toward a terminus in the Black Sea. In the upper region of the Danube, though, where the river emerges from the Black Forest in Germany, water from the river seeps into the fractured bedrock underlaying the river and travels through the fractures into the Rhine River basin, thus flowing toward a terminus in the North Sea.

Again, the need to understand this relationship in the context of regulating, managing, and preserving water resources cannot be overemphasized. In fact, aside from a few island-nations, virtually every nation shares a ground-water system with one or more countries, and the majority of ground-water systems are related or linked directly to surface water resources. Thus, this relationship has serious domestic and international implications. And, as will be further discussed, it is such basic scientific knowledge that appears to be lacking in the development of policies, laws, and management schemes related to water resources.

Confined and Unconfined Ground-Water Aquifers

Lastly, I would like to describe two of the most common types of ground-water aquifers. Watertable or unconfined aquifers are aquifers whose watertable (top boundary of the aquifer) are generally found relatively close to the land surface, and which contain layers of materials of high permeability extending from the land surface to the impermeable base of the aquifer. Recharge to such aquifers is mostly from the downward seepage of local precipitation and runoff percolating through the soil just above the ground-water table, or through lateral ground-water flow. Thus, the residence time of water in an unconfined aquifer may range from days to years. Confined or artesian aquifers are aquifers overlain by strata of practically impermeable or low-permeability strata. Such aquifers are recharged through lateral flow of water from the recharge zones - surface areas, usually at distant higher elevations in the mountains or on high plateaus where the aquifer crops out on the land surface. Thus, the residence time of water in a confined aquifer generally ranges from centuries to eons.

As we are discussing dispute prevention and development in the context of water resources, I would point to two examples of such aquifers in the Middle East, a region known for its disputes as well as its great need for efficient development of water resources. In northeastern Africa, for example, underneath the countries of Chad, Egypt, Lybia, and Sudan, lies an unconfined aquifer in the Nubian Sandstone formation. The ground-water table of this aquifer is found at depths ranging from a few meters (e.g., in deflated depressions in the oases of the Northeastern Sahara) down to a few hundred meters (e.g., in the Northern Sinai Peninsula). The water content in this aquifer is estimated to be at least 15,000 years old when, having percolated down during the glaciation of northern and central Europe, the shift in climatic zones brought much rain and possibly even snow into this currently parched region. While the overlaying strata are still relatively permeable, present-day recharge rates range from minimal in some regions to nil in others. Moreover, this aquifer is not related or connected to any other water resource in the region.

Underlying the West Bank (or as named by the Israelis, the Judea and Samaria region) and the foothills bordering the Israeli coastal plain and the Jordan-Dead Sea rift valley, lies the Judean Mountain or West Bank aquifer. This aquifer is particularly interesting in that it is both an unconfined and a confined aquifer. It begins as an unconfined aquifer in the highlands of the Judean Mountains where precipitation, mostly in the form of rain, recharges the aquifer. Moving westward toward the Mediterranean Sea, as the aquifer follows the downward curvature of the strata, it becomes a confined aquifer due to more impermeable, confining material lying above the aquifer. Thus, precipitation falling on the lowlands generally does not reach the aquifer, but flows toward another unconfined aquifer known as the coastal aquifer on the edge of the Mediterranean Sea. Moving eastward from the mountains, toward the Jordan-Dead Sea rift valley, the aquifer again becomes confined underneath low-permeability strata, and eventually reaches the Jordan River, the Dead Sea, and various freshwater springs found along the Jordan rift valley.

Hydrologic Reality and the UN Convention

The UN Convention on the Law of the Non-Navigational Uses of International Watercourses was developed to promote sustainable development and protection of global water supplies, as well as to help prevent and resolve conflicts over transboundary water resources. Thus, the Convention offers principles - such as equitable and reasonable use and no significant harm - by which States are to conform their conduct, especially when dealing with water resources that traverse international boundaries.

The relevance of the scientific background provided earlier to the UN Convention is rather clear, given that the Convention purports to provide guidelines pertaining to the use, management, and preservation of a portion of the hydrologic cycle. Upon close review, however, the Convention's foundation must be questioned, especially when considered in the context of hydrologic reality - water resources are inextricably linked and piecemeal governance of such resources is inappropriate and inadequate to meet the present and future needs of sustainable use.

This is especially apparent in the defined scope of the Convention, provided in Articles 1 and 2. While Article 1 limits application of the Convention's provisions only to "international watercourses," Article 2 defines "watercourse" as: "a system of surface waters and ground-waters constituting by virtue of their physical relationship a unitary whole and normally flowing to a common terminus."

Although this definition appears innocuous, it is important to point out what is not included in the definition. First, it does not include related water resources which do not "flow to a common terminus." As noted earlier, downward flow is dependent on gravity, soil permeability, and presence of obstacles (e.g., low-permeability geologic formation). Therefore, it is not uncommon to have related surface- and ground-waters (such as a stream and an underlaying aquifer) flowing in different geographical directions and toward different termini. Thus, under the Convention, any use or management scheme developed for the stream would not be bound by the Convention's principles with regard to the underlaying ground-water. Depending on the scheme developed, it could reasonably raise both quality and quantity concerns for those relying on the ground-water. Nonetheless, the scheme's proponents would not be obligated to take those concerns into account. Given that nearly every country in the world shares a ground-water system with one or more countries, such a situation is nothing if not troubling.

Secondly, and as a direct extension of the first point, the definition excludes water resources that are indirectly related. For example, a third water resource linked to the above-described aquifer is only indirectly linked to the above-described stream. Even if the aquifer did flow toward a common terminus, a third water resource directly related to the aquifer but not the stream would likewise be indirectly related to the stream. Thus, any use or management scheme developed for the stream would not have to consider the effects of the scheme on the indirectly related water resources, again implicating the potential for transboundary disputes over the effects of the scheme on water quality and quantity.

Finally, the Convention excludes from the scope of "watercourse" ground-water aquifers unrelated to surface waters. In the context of hydrologic reality, this limitation ignores regions where surface water is sparse or nonexistent, such as arid and desert environments, where ground-water aquifers often traverse international boundaries. Significantly, the more immediate problem of this definition has been the apparent misunderstanding, misuse, and misapplication of hydrologic and hydrogeologic terminology, in the context of this definition, by the UN's International Law Commission which developed the Convention. In noting the Commission's unwillingness to include unrelated ground-water within the scope of the Convention, a past rapporteur of the Commission misdefined "so-called confined ground water, that is, ground water that is not related to surface water." (McCaffrey, at 403). The inaccuracy lies in the fact that confined aquifers can be, and often are, related to surface waters. While seemingly just a minor technical infraction, the result of this and other minor misstatements has led to further misuses of definition and misapplications of the Convention's scope by a number of legal scholars. Moreover, that such an error occurred at the United Nations questions the actual understanding of hydrologic reality by the Commission's drafters.

The resulting problem with these limitations is twofold. First, there is the potential for states to embark on strategies designed to use, regulate, or manage a particular water resource without regard to the consequences such action might effect on related but excluded water resources. Secondly, and possibly more damaging, it permits the possibility that related water resources will be used, regulated, or managed under different systems that profess disparate objectives and that may be incompatible or conflicting.

As mentioned earlier, the Nubian Sandstone Aquifer, underlaying Chad, Egypt, Lybia, and Sudan, is unrelated to any surface water resource in the region. Any recharge that does occur is negligible and is the result of occasional rains and the rare flash flood. Hence, this aquifer fails to fit under the UN Convention's narrow definition of international watercourse. It is not part of a "system of surface and groundwaters [sec] constituting by virtue of their physical relationship a unitary whole." Moreover, and as a result of the lack of such an interaction with surface water, the water in the aquifer is nearly stagnant and does not flow into a "common terminus" with any surface water. Consequently, any scheme designed to exploit or manage the aquifer by one or more of the four nations sharing the resource would be exempt from abiding by the principles contained in the Convention, regardless of the potential or actual consequences to the quality or quantity of the water in the aquifer.

Application of the UN Convention to conflicts or water use strategies over the Judean Mountain aquifer is likewise questionable, in large part, because it is unclear how the Convention would treat a single aquifer (or even directly related aquifers) flowing toward different termini.(1) The Judean Mountain aquifer is an unconfined aquifer in the highlands, and a confined aquifer along the westward and eastern slopes. While most of the water flow in the aquifer is westward, some water does flow eastward toward a different terminus and supplies the various freshwater springs that are found along the Jordan rift valley, most notable Ein-es-Sultan in Jericho, and a host of fresh to saline springs along the banks of the Dead Sea. That any surface waters may be directly related to the Judean Mountain aquifer would further complicate the scenario insofar as such surface waters would also flow toward two divergent termini. Thus, it is possible that a water use or management strategy implemented in the highlands region, depending on specific location and purpose, might be exempt, to varying degrees, from abiding by the principles of the Convention with regard to the aquifers found in the lower regions.

Still another example of transboundary water resources clearly falling outside the scope of the UN Convention is the upper Danube River region where the river emerges from the Black Forest in Germany. Water from the Danube River seeps here into the fractured bedrock underlaying the river and travels through the fractures into the Rhine River basin. Thus, while the water in the Danube channel flows toward a terminus in the Black Sea, some of the same water escapes through the river bed as ground water and flows to the Rhine River basin with its terminus in the North Sea. Any use or management scheme of the Danube River in this region would therefore be exempt from the Convention's obligations with regard to any possible consequences effected on the Rhine River.


The significance of understanding the science underlying any use, management, or conservation strategy aimed at surface- or ground-water resources is readily apparent given the nature of water resources and the inextricable relationship found between such resources. However, such understanding is also an absolute imperative when developing and formulating regulatory schemes and guidelines for the purpose of promoting sustainable development and protecting transboundary water resources. The lack of a more comprehensive and hydrologically sound application of the UN Convention to interrelated water resources suggests that the Convention was formulated without a firm understanding of hydrologic reality.

Where does that leave us? It is quite possible that the utility of the UN Convention initially will be limited, and will prove inadequate for achieving its stated objectives. The Convention, however, is a framework document, such that future agreements and policies may be developed under its wingspan. For that reason, there is hope that future elaborations and amendments will expand that wingspan to incorporate a more scientifically reasonable approach for global water management.

As science develops and operates on the frontiers of knowledge, the law must keep apace and must continue to adapt to new scientific discoveries and developments. Moreover, the technical and scientific community must become more involved in the political, legislative and judicial process, and must be embraced by those communities so as to ensure that the development of policies, regulations, and management and conservation schemes do comport with the realities of science. Only through a full understanding of the various legal, social, policy, economic, and of course, scientific issues involved, will states be able to use, manage, and protect their shared resources appropriately and effectively, and in such a way that the resources suffice for present needs and are preserved for future generations.


Barberis, Julio, International Groundwater Resources Law, UN Food and Agriculture Organization Legis. Study No. 40, at 1 (1986)

Bouwer, Herman, Groundwater Hydrology 2-3 (1978)

Eckstein, Gabriel and Eckstein, Dr. Yoram, International Water Law, Transboundary Groundwater Resources and the Danube Dam Case, in Gambling with Groundwater-Physical, Chemical, and Biological Aspects of Aquifer-Stream Relations (Brahana et.al. Eds.), p. 243 (paper and presentation for International Association of Hydrologists XXVII Congress and Annual Meeting of the American Institute of Hydrology, Las Vegas, Sept. 27 - Oct. 2, 1998)

Gleick, Peter H., The World's Water 1998-1999: The Biennial Report on Freshwater Resources, Island Press (1998)

Hayton, Robert D., Doman Colloquium on the Law of International Watercourses: Review of the ILC's Draft Rules on the Non-Navigational Uses of International Watercourses - Observations on the International Law Commission's Draft Rules on the Non-Navigational Uses of International Watercourses: Articles 1-4, 3 Colo. J. Int'l Envt'l L. & Pol'y 31 (1992)

McCaffrey, Stephen C., Current Development: The International Law Commission Adopts Draft Articles on International Watercourses 89 A.J.I.L. 395, 403 (1995)

United Nations, 1997, Convention on the Law of the Non-Navigational Uses of International Watercourses, Int'l Legal Material vol. 36, p. 700 (May 1997)

Winter, Thomas C., et. al., Ground Water and Surface Water: A Single Resource, U.S. Geological Survey Circular 1139 (1998)

World Resources Institute, United Nations Environmental Programme, United Nations Development Programme, World Resources 1992-93: A Guide to the Global Environment 75 (1992)

1. Arguably, the UN Convention might not be applicable to the situation of the West Bank aquifer given the debatable political status of the West Bank and the Palestinian controlled territories under international law. Nonetheless, the situation provides an excellent example of disputed water needs and objectives in a political geography that, were it to be construed a transboundray dispute, whether now or in the future, would likely fall outside of the scope of the UN Convention.

Reprinted with the kind permission of the American University Center for the Global South, Washington, D.C.  Any use of this article must include the appropriate citation:

Gabriel E. Eckstein, Hydrologic Reality: International Water Law and Transboundary Ground-Water Resources, paper and lecture for the conference on "Water: Dispute Prevention and Development" American University Center for the Global South, Washington, D.C. (October 12 - 13, 1998)