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The Law of International Watercourses, 3rd Edition by McCaffrey, Stephen C

Part IV Fundamental Rights and Obligations, A Substantive Obligations, 9 Equitable and Reasonable Utilization

From: The Law of International Watercourses (3rd Edition)

Stephen C. McCaffrey

From: Oxford Public International Law (http://opil.ouplaw.com). (c) Oxford University Press, 2015. All Rights Reserved. Subscriber: null; date: 01 April 2020

Freshwater — International co-operation — Lakes — Rivers

(p. 444) Equitable and Reasonable Utilization


Born largely of the U.S. Supreme Court’s decisions in interstate apportionment cases beginning in the early twentieth century,2 and supported by decisions in other federal states,3 the doctrine of equitable utilization was applied to international watercourses as the basic, governing principle by the International Law Association’s (ILA’s) 1966 Helsinki Rules.4 Its status as the fundamental norm in the field has recently been confirmed by the decision of the International Court of Justice (ICJ) in the Case concerning the Gabčíkovo-Nagymaros Project (Hungary/Slovakia).5 (p. 445) As indicated in Chapter 8, the 1997 UN Convention also appears to treat equitable utilization as the overarching principle governing the use of international watercourses, as did the draft articles adopted by the ILC on second reading in 1994.6 The authorities supporting this principle have been discussed at length elsewhere,7 and its theoretical basis has been explored in section C of Chapter 4. The present chapter will therefore confine itself principally to an examination of the concept of equitable utilization and of how the doctrine operates in practice.

It should be noted at the outset that equitable utilization is chiefly a doctrine governing apportionment, or allocation, of water between states sharing an international watercourse. Indeed, it is normally referred to in decisions of the U.S. Supreme Court, where it has been developed in the greatest detail, as the doctrine of equitable “apportionment.” As will be seen presently, any harm sustained by one state or another, as a result of an insufficient quantity of water, plays only a subsidiary role in the process of arriving at an equitable allocation. As human activities have increasingly resulted in pollution and other adverse effects on water quality and ecosystems, they have come under regulation by municipal and, to a lesser extent, international law. These regulatory regimes have, however, largely been separate from those governing allocation of water quantity, particularly on the national level. The preferable approach would clearly be a holistic one, which explicitly takes into account considerations of both allocation and protection. On the international plane, the concept of equitable utilization itself has, to some extent, been asked to perform both of these functions,8 which has resulted in a degree of confusion and perhaps in an overloading of a principle whose implementation is already a complex matter. Is it asking too much of the doctrine of equitable utilization to expect it to address problems of both water quantity and quality? Is there an “equitable right to pollute” and an “equitable obligation not to pollute” beyond a certain level, or is pollution governed by a separate set of international norms? To what extent is pollution governed not by the principle of equitable utilization, but by the no-harm rule? If it is governed by the former, is pollution harm simply one factor to be taken into account in the equitable allocation process, or is it subject to discrete regulation outside the equitable allocation calculus? These questions will be addressed in the following two chapters. The present chapter will focus upon the norm of equitable utilization as it relates to quantitative allocation. This should not be taken to imply that Article 5 of the UN Watercourses Convention, “Equitable and Reasonable Utilization and Participation,” does not deal with other matters, however.

(p. 446) A.  The Concept of Equitable Utilization

The philosophical and policy underpinnings of the principle of equitable utilization were well stated by Justice Oliver Wendell Holmes in the case of New Jersey v New York, decided by the U.S. Supreme Court in 1931.9 In that case New Jersey, the lower riparian, sought to enjoin New York from diverting waters of the Delaware River, its tributaries or headwaters, to increase the water supply of New York City. In discussing the rule of law to be applied, Justice Holmes stated as follows:

A river is more than an amenity, it is a treasure. It offers a necessity of life that must be rationed among those who have power over it. New York has the physical power to cut off all the water within its jurisdiction. But clearly the exercise of such a power to the destruction of the interest of lower States could not be tolerated. And on the other hand equally little could New Jersey be permitted to require New York to give up its power altogether in order that the river might come down to it undiminished. Both States have real and substantial interests in the River that must be reconciled as best they may. The different traditions and practices in different parts of the country may lead to varying results but the effort always is to secure an equitable apportionment without quibbling over formulas.10

A river is a “treasure” that “offers a necessity of life.” Therefore, when it flows through more than one jurisdiction, it “must be rationed among those who have power over it.” It would be intolerable for the upstream state to cut off all the water from the downstream state, or for the latter to require the former to “give up its power altogether.” Thus, Holmes effectively rejects both the absolute territorial sovereignty and the absolute territorial integrity theories.11 He recognizes that “both states have real and substantial interests” and that these interests “must be reconciled as best they may,” rather than simply declaring one state the absolute winner and the other the absolute loser. The object of this process of reconciliation “always is to secure an equitable apportionment.”

The same court shed further light on the workings of the equitable apportionment doctrine in a 1945 decision concerning the allocation of the water of the North Platte River.12 The North Platte rises in Colorado and flows from that state through Wyoming and into Nebraska. Nebraska, whose uses (or “appropriations”) had generally been prior in time, alleged that diversions for irrigation purposes in Wyoming and Colorado deprived Nebraska of water for its own irrigation projects to which it was equitably entitled. In the following passage, the Court explained the relevance of priority of use, and its relation to other factors, in arriving at an equitable allocation:

Apportionment calls for the exercise of an informed judgment on a consideration of many factors. Priority of appropriation is the guiding principle.13 But physical and climatic (p. 447) conditions, the consumptive use of water in the several sections of the river, the character and rate of return flows, the extent of established uses, the availability of storage water, the practical effect of wasteful uses on downstream areas, the damage to upstream areas as compared to the benefits to downstream areas if a limitation is imposed on the former—these are all relevant factors. They are merely an illustrative, not an exhaustive catalogue. They indicate the nature of the problem of apportionment and the delicate adjustment of interests which must be made.14

Thus, equitable apportionment of shared water resources requires taking into consideration all relevant factors. While priority of use is an important consideration, priority alone is not decisive; even less is the place where the watercourse system originates controlling.15 In addition, this decision as well as others of the U.S. Supreme Court16 illuminate the meaning of “harm,” or damage, in the context of allocation of shared water resources: they signal a recognition that just as a downstream state may be harmed by uses upstream, so also may an upstream state be harmed if its use is limited in favor of a state downstream. This phenomenon, the implications of which are explored further in the following two chapters, demonstrates what Ronald Coase described as the “reciprocal nature” of the problem.17 Since both states may be harmed, harm alone cannot be the decisive criterion. The objective is to find a balance that results in the least harm to each, or which includes some form of compensation for the state that bears the greater portion of the harm.18 Arriving at this balance may, particularly in areas of water shortage, necessitate the taking of measures to conserve water and to increase efficiency of use.19

In a later decision, the Court summed up the doctrine, and the process it requires, as follows: “It is a flexible doctrine which calls for ‘the exercise of an informed judgment on a consideration of many factors’ to secure a ‘just and equitable’ allocation.”20 Thus, the lodestar is not simply who got to the river first, or who is upstream and who downstream, but what is equitable and reasonable under the circumstances. No state has an inherently superior claim. The doctrine is “flexible” in this sense and also in a temporal sense: what is an “equitable apportionment” may change over time.

(p. 448) The temporal flexibility of the principle is well illustrated by the U.S. Supreme Court’s first equitable apportionment decision, Kansas v Colorado.21 In that case, the Court found that Kansas, the lower riparian and prior user, was not entitled to relief against Colorado for the latter’s diversions of water from the Arkansas River, which had caused “perceptible injury to portions of the Arkansas valley in Kansas . …”22 The Court “compare[d] the amount of this detriment with the great benefit which has obviously resulted to … Colorado”23 and found that “equality of right and equity between the two states forbids any interference with the present withdrawal of water in Colorado for purposes of irrigation.”24 However, the Court went on to say: “it is obvious that if the depletion of the waters of the river by Colorado continues to increase there will come a time when Kansas may justly say that there is no longer an equitable division of benefits, and may rightfully call for relief against the action of Colorado . …”25

This case well illustrates the different effects of the equitable utilization principle and the no-harm doctrine, at least as the latter is often perceived: as discussed below, if the no-harm principle, in its strictest form, had been the governing rule, Kansas would presumably have prevailed, on the ground that Colorado’s new use caused “perceptible injury” to Kansas’ established uses. Indeed, at least at first blush, Kansas appears to have relied on the no-harm, or sic utere tuo principle when it “insisted that Colorado … is violating the fundamental principle that one must use his own so as not to destroy the legal rights of another.”26 But if Kansas’ contention is examined closely, it will be seen to be fully compatible with the equitable apportionment doctrine articulated in the Supreme Court’s judgment. For Kansas argued not that Colorado may not cause it factual harm, but that Colorado may not “destroy [its] legal rights” (emphasis added). It was precisely to determine what its legal rights were that the case was brought to the Supreme Court. And the Court answered, in effect, that Kansas had a legal right to an equitable apportionment of the river’s benefits, a share that Colorado had not intruded upon, even though its later use of the river had caused Kansas factual harm.

This distinction between factual harm and legal injury is crucial to an understanding of the principle of equitable utilization. As Bourne has noted: “The unqualified statement that whatever causes damage to another is unlawful and must be paid for is patently unsound.”27 It is only injury to a legally protected interest that is prohibited. According to the doctrine of equitable utilization, each state has a legally protected interest in an equitable share of the uses and benefits of an international watercourse. Again, the U.S. Supreme Court’s opinion in Kansas v Colorado is instructive. Here the Court quoted from a mid-nineteenth century decision:

[T]he right to the reasonable and beneficial use of a running stream is common to all the riparian proprietors, and so, each is bound so to use his common right, as not essentially to prevent or interfere with an equally beneficial enjoyment of the common right, by all (p. 449) the proprietors . … It is, therefore, only for an abstraction and deprivation of this common benefit, or for an unreasonable and unauthorized use of it, that an action will lie.28

Thus, again, while harm is an important factor to be taken into consideration, it is not factual harm per se, but deprivation of a state’s equitable share, that is prohibited. And the definition of that share may change over time, with changes in the circumstances of the states concerned, water supply (due, for example, to climate change29) and even technological possibilities for greater efficiency and conservation.30

Another feature of the above quotation bears scrutiny: its emphasis on the reasonableness of use. If a riparian uses its share unreasonably, “an action will lie”—that is, the riparian will have exceeded its right. There are few examples in international jurisprudence of what constitutes an unreasonable use of shared freshwater resources. However, it is not difficult to imagine possibilities, including wasteful uses, sale of withdrawn water outside the basin, excessive withdrawals for use by the withdrawing state outside the basin, serious pollution of the watercourse, as by toxic or hazardous substances, and the like. The fundamental requirement of international law is that a state’s use of an international watercourse be both equitable and reasonable. Therefore, it is not only the quantity of water that is involved, but also what the state in question does with the water that is addressed by the equitable-and-reasonable standard.

An important basis of the entitlement to an equitable share is the notion of equality of right. This principle was recognized by the Permanent Court of International Justice (PCIJ) in its 1929 decision in the River Oder case31 and confirmed recently for non-navigational uses by the ICJ in the Gabčíkovo-Nagymaros case:32

[the] community of interest in a navigable river becomes the basis of a common legal right, the essential features of which are the perfect equality of all riparian States in the user of the whole course of the river and the exclusion of any preferential privilege of any one riparian State in relation to the others . …

Modern development of international law has strengthened this principle for non-navigational uses of international watercourses as well . …33

In Kansas v Colorado, the U.S. Supreme Court had the following to say about the role of the principle of equality of right in reconciling the interests of two American states: “One cardinal rule, underlying all the relations of the States to each other, is (p. 450) that of equality of right. Each State stands on the same level with all the rest. It can impose its own legislation on no one of the others, and is bound to yield its own views to none.”34 In a later decision, the court further explained that settlement of water disputes on the basis of equality of right does not mean:

that there must be an equal division of the waters of an interstate stream among the States through which it flows. It means that the principles of right and equity shall be applied having regard to the “equal level or plane on which all the States stand, in point of power and right, under our constitutional system” …35

These statements are equally applicable on the international plane where, as discussed below, they are based on notions of sovereign equality of independent states rather than on the equality of quasi-sovereign units of a federal state under its constitutional system.

Similarly, in the early Swiss case of Aargau v Zurich36 (the “Zwillikon Dam case”), the Swiss Federal Court in 1878 elucidated the meaning of this principle in the context of shared water resources when it stated:

In the case of public waters which extend over several cantons and, therefore, belong to several cantons, it follows from the equality of the cantons that none of them may, to the prejudice of the others, take such measures upon its territory, as the diversion of a river or brook, construction of dams, etc., as may make the exercise of the rights of sovereignty over the water impossible for the other cantons, or which exclude the joint use thereof or amount to a violation of territory. On the other hand, regardless of this, no canton has, in its relation to the other cantons, the right of adapting the exercise of the sovereign rights over the water to its wishes and special needs, regardless of how desirable and expedient the establishment of uniform principles in such cases might be.37

The Court went on to draw a distinction between private ownership and sovereignty in the context of multi-jurisdictional waters:

With regard to public waters, the cantons have no private ownership, but only sovereignty, from which is not in any way derived any right by which in some instances the canton situated up-stream could be entirely deprived of the use of the water or, at least, of a certain manner of use. Each canton is rather entitled, by virtue of its sovereignty, to take the necessary measures for a rational utilization of the public waters, corresponding to its needs, but only in so far … as the joint use of the water is not thereby made impossible but is left to the rest of the cantons in the same manner.38

Thus, most interestingly, unlike Attorney-General Harmon in his 1895 opinion concerning the Rio Grande,39 the Swiss Federal Court derived from the principle of sovereignty not at all an absolute right to dispose of the water regardless of the effects on other jurisdictions, but rather an obligation to recognize the equal sovereignties (p. 451) of the other jurisdictions (there, cantons) through which the water flowed. The same idea was expressed by Oppenheim in the first edition of his classic work, published in 1905:

[T]erritorial supremacy does not give a boundless liberty of action. Thus, by customary International Law, … a State is, in spite of its territorial supremacy, not allowed to alter the natural conditions of its own territory to the disadvantage of the natural conditions of a territory of a neighbouring state—for instance, to stop or divert the flow of a river which runs from its own into a neighbouring territory.40

This was an important statement, by one of the leading authorities in the field at the time, and made well before the development of, for example, international human rights law, and thus at a time when it was only dimly recognized that international law could regulate matters within a state’s territory.

As already suggested, the idea of equality of right has much in common with the principle of the sovereign equality of states, enshrined in Article 2(1) of the United Nations Charter. However, merely recognizing that states have equal rights usually does not, by itself, solve the problem of apportioning the uses and benefits of an interstate or international stream. It is only the starting point. But it is an essential starting point, because it means that no state has an inherently superior claim to the use of the watercourse. If, for example, there are two states through which a successive international watercourse flows, the rights of each in the watercourse are equal to those of the other. One of them may not destroy the rights of the other by using some or all of the waters of the river, whether that use be prior or subsequent to the use of the other state. Indeed, in the Zwillikon Dam case, it was the downstream jurisdiction that was the prior user and claimed a right to the flow of the river unaffected by a later upstream dam.

On the other hand, as has already been seen, equality of right does not mean an entitlement to an equal share of the water. Neither the ICJ nor the U.S. Supreme Court nor any other tribunal of which the author is aware has come to this conclusion. Instead, they have in effect recognized what the ICJ recently described as the “basic right to an equitable and reasonable sharing of the resources of an international watercourse.”41 These “resources”42 include not only the water, per se, but also, for example, the capacity of the water to produce hydroelectric power—flowing water’s “motive force”— fish, recreational benefits, the ecological integrity of the watercourse system,43 and most fundamental of all, water for drinking and (p. 452) general sustenance. Thus, each state has an equal right to an equitable share of the uses and benefits of the stream. The challenge is the reconciliation of the equal rights of riparian states, that is, the determination of each state’s equitable share—or, more broadly, the determination of whether each state’s conduct or use is equitable and reasonable vis-à-vis its co-riparians. For “equity” is necessarily a relative concept. Whether a state’s use is equitable and reasonable can be determined only by taking into account the uses and needs of its co-riparians.

In this connection, the litigation in the U.S. Supreme Court between the states of Colorado and New Mexico over the Vermejo River is illustrative.44 The Vermejo is a small river that rises in Colorado and flows into New Mexico, joining the Canadian River some 55 miles downstream. But even a small river can take on very large importance in arid areas, as the Silala case currently before the International Court makes plain.45 The U.S. Supreme Court noted that: “The major portion of the river is located in New Mexico. The Colorado portion consists of three main tributaries that combine to form the Vermejo River approximately one mile below the Colorado-New Mexico border.”46 While the river had not been utilized in Colorado, in New Mexico “farmers and industrial users [had] diverted water from the Vermejo for many years.”47 Thus, the case was a typical one of earlier development of shared water resources by a downstream state and subsequent plans to utilize the water in an upstream state.

In 1975, Colorado authorized a diversion from the river by a steel company, which planned to transfer the water into the basin of the Purgatoire River in Colorado for industrial development and other uses. This prompted the four principal users in New Mexico48 to file suit in federal court seeking to enjoin any diversions in Colorado by the steel company. The trial court granted the requested relief49 but the court of appeal stayed the action on the ground that the U.S. Supreme Court had in the meantime decided to hear a case concerning the river between the two states, Colorado v New Mexico,50 brought to it under its original jurisdiction. As is its practice in such cases, the Court appointed a special master to conduct trial proceedings and recommend a resolution.

The special master found that “the entire available supply is needed to satisfy the demands of appropriators in New Mexico with senior rights.”51 This means that if a strict rule of priority were followed, Colorado would not be permitted to divert any water. But, applying the Court’s equitable apportionment case law, the special master recommended that the Court allow Colorado to withdraw 4,000 (p. 453) acre-feet of water per year (AFY)52 for the inter-basin diversion project.53 According to the Court:

The Special Master’s recommendation appears to rest on two alternative grounds: first, that New Mexico could compensate for some or all the Colorado diversion through reasonable water conservation measures; and second, that the injury, if any, to New Mexico would be outweighed by the benefit to Colorado from the diversion.54

The Supreme Court reaffirmed the applicability of the doctrine of equitable apportionment and rejected two positions at opposite polar extremes: New Mexico’s argument that priority of use was controlling,55 and any suggestion that the mere fact that the Vermejo rises in Colorado automatically entitles Colorado to a share of its water.56 However, the Court concluded it needed additional findings of fact to enable it to determine whether the special master had correctly applied the principle of equitable apportionment to the facts of the case. It therefore remanded the case to the special master to make those further findings.

In discussing the doctrine of equitable apportionment, the Court reaffirmed that all relevant factors must be considered “in arriving at ‘the delicate adjustment of interests which must be made.’ ”57 It noted that under its prior decisions, “equitable apportionment will protect only those rights to water that are ‘reasonably required and applied,’ ”58 shedding light on the meaning of “reasonable” utilization. The Court continued:

Especially … where water is scarce, “[there] must be no waste … of the ‘treasure’ of a river . … Only diligence and good faith will keep the privilege alive.”59 … Thus, wasteful or inefficient uses will not be protected . … Similarly, concededly senior water rights will be deemed forfeited or substantially diminished where the rights have not been exercised or asserted with reasonable diligence.60

While the latter statement smacks of a “use-it-or-lose-it” principle, the Court’s overall approach is more compatible with an interpretation under which it is only “existing uses” that are actually being engaged in that will be protected, and that weight will not be given in the balancing process of equitable apportionment to uses that have been abandoned or even neglected. But because of the flexible character (p. 454) of the equitable utilization doctrine, it seems apparent that failure to continue to make uses with reasonable diligence would not prevent the former user from making a claim in the future to a right to an equitable share of the uses and benefits of the stream. This would then be more of an uphill battle than would have been the case if the use had not been given up in the first place, however.

With regard to conservation of water or efficiency of use, the Court explained that states have “an affirmative duty to take reasonable steps to conserve and augment the water supply of an interstate stream.”61 This means that they have a “duty to employ ‘financially and physically feasible’ measures ‘adapted to conserving and equalizing the natural flow.’ ”62 With regard to the idea that New Mexico should not have to implement conservation measures so that Colorado could make its proposed use, the Court quoted the following passage from its 1922 decision in Wyoming v Colorado: “The question here is not what one State should do for the other, but how each should exercise her relative rights in the waters of this interstate stream . … [E]ach of these States [has] a duty to exercise her right reasonably and in a manner calculated to conserve the common supply.”63 This means that states in the position of Colorado who wish to make new uses must also “undertake … reasonable steps to minimize the amount of diversion that will be required.”64

The special master had found that the use of Vermejo water by one of the New Mexico entities in particular65 was inefficient and resulted in waste. He therefore concluded that New Mexico could compensate for a diversion in Colorado of 4,000 AFY through conservation measures. While the Court had no difficulty with this conclusion in principle, it remanded the case to the special master for additional factual findings on a number of points, including: “the extent to which reasonable conservation measures in both States might eliminate waste and inefficiency in the use of water from the Vermejo River;”66 and whether a diversion in Colorado would materially affect New Mexico in view of possible water conservation measures that could be taken there.

The Court also reaffirmed the notion that “in an equitable apportionment of interstate waters it is proper to weigh the harms and benefits to competing States.”67 It confirmed that “the equities supporting the protection of existing economies will usually be compelling”68 but recognized that: “Under some circumstances … the countervailing equities supporting a diversion for future use in one State may justify the detriment to existing users in another State.”69 The Court gave as an example a situation in which the state proposing a diversion clearly demonstrates that “the (p. 455) benefits of the diversion substantially outweigh the harm that might result.”70 And, tying the harm/benefit analysis into the duty to conserve water supplies, the Court indicated that in deciding whether the proposing state had made this showing, “an important consideration is whether existing users could offset the diversion by reasonable conservation measures to prevent waste.”71 The Court noted that such an approach is consistent with its “emphasis on flexibility in equitable apportionment and also accords sufficient protection to existing uses.”72 But the Court did not believe it had sufficient facts to determine whether the special master had correctly weighed the harm and benefits and accordingly requested him to make additional findings relating to these points, as well.73

When the case came back to the Court, the principal question was whether Colorado had met its burden of proof.74 The Court held that Colorado must demonstrate its right to divert Vermejo waters by “clear and convincing evidence.” This is a higher standard than that applied in the ordinary civil case, where a “preponderance of the evidence” standard is typically applied. The Court set a high standard because of the “unique interests involved in water rights disputes between sovereigns.”75 According to the Court, the applicable evidentiary standard meant that “Colorado’s diversion should and will be allowed only if actual inefficiencies in present uses or future benefits from other uses are highly probable.”76

The Court found that Colorado had not met its burden of proving that a diversion should be permitted.77 Not only did Colorado fail to point to specific measures New Mexico could take to conserve water and preserve existing supplies, it also failed to provide evidence that it had “undertaken reasonable steps to minimize the amount of the diversion that will be required.”78 In fact, the Court noted that there was no evidence that the Colorado steel company seeking the diversion had decided upon “a definite or even tentative construction design or plan, or that it has prepared an economic analysis of its proposed diversion.”79 The Court was of the view that “it would be irresponsible of us to apportion water to uses that have not been, at a minimum, carefully studied and objectively evaluated, not to mention decided upon.”80 Thus, Colorado had failed to specify the benefits that the proposed diversion would (p. 456) bring. New Mexico, in contrast, had “attempted to identify the harms that would result from the proposed diversion”81 through the commissioning of independent economic studies.

Finally, the Court referred to the special master’s observation that some three-fourths of Vermejo River water is produced in Colorado, and that this had led him to conclude that “the equities are with Colorado, which requests only a portion of the water which it produces.”82 The Court pointed out that in its prior decision in the case it had “rejected the notion that the mere fact that the Vermejo River originates in Colorado automatically entitles Colorado to a share of the river’s waters.”83 It concluded that equitable apportionment “should turn on the benefits, harms, and efficiencies of competing uses, and … the source of the Vermejo River’s waters should be essentially irrelevant to the adjudication of these sovereigns’ competing claims.”84

For the foregoing reasons, the Court concluded that Colorado had not met its burden of proof and dismissed the case.85 However, it left the door slightly open for Colorado, suggesting that a showing that circumstances had changed might justify a diversion. Until that time, however, the Court emphasized that “the equities compel the continued protection of the existing users of the Vermejo River’s waters.”86

Colorado v New Mexico thus presents the classic case of an upstream state wishing to make use for the first time of a watercourse that had been fully utilized by a downstream state. It is, of course, a case involving constituent units of a federation. Caution must therefore be exercised in drawing analogies between this case and controversies among different countries over internationally shared water resources. However, certain lessons concerning the functioning of the principle of equitable utilization may be drawn from the decision. This is all the more true in view of the Supreme Court’s sensitivity, in this as in all of its other interstate apportionment decisions, to the fact that it was dealing with a controversy between “sovereigns.” While the doctrine developed by the U.S. Supreme Court is styled “equitable apportionment” and deals largely with the allocation of water quantities between U.S. states, there are no significant differences between that doctrine and the broader principle of equitable and reasonable utilization, insofar as allocation of shared water supplies is concerned.

Colorado v New Mexico teaches that according to the principle of equitable utilization, each state has an equal right to an equitable portion of the uses and benefits (p. 457) of a shared watercourse, irrespective of where the watercourse rises or which state’s use was prior in time. New upstream uses may be permissible even where existing downstream uses fully consume the stream’s waters. This may be the case, for example, where the benefits of a new use (e.g., providing food and electricity needed to alleviate poverty in the state making the use) substantially outweigh the harm that might result from it (e.g., reduction in the production of agricultural products for export in a state with relatively high living standards). However, the burden is on the state proposing the new use to demonstrate that this is the case. An important consideration in this regard is whether existing users could compensate for the loss due to the new use through reasonable conservation measures.

The harm-benefit balancing test was applied in the Supreme Court’s very first equitable apportionment decision87 and is an integral part of the equitable utilization analysis. It will perhaps be more difficult to apply where nation states are involved, but the principle that one state may have to bear some harm to an existing use, in some cases with appropriate compensation, to allow another state to initiate a use giving rise to substantial benefits, is recognized at least implicitly by the UN Watercourses Convention.88 Like Colorado v New Mexico, the Convention also recognizes that conservation of water and avoidance of waste are factors to be taken into consideration in arriving at an equitable allocation.89 For example, to accommodate a lower riparian state’s intensive use with an upper riparian’s planned new use, the equitable utilization principle may require the lower riparian to increase the efficiency of its water usage or to conserve and augment water supplies through such means as treatment of wastewater. Efficiency and conservation would also be required of the upper riparian, of course, to minimize the impact of its new use upon established uses downstream.

There is additional support in state practice for the principle that prior, or existing uses are not entitled to absolute protection.90 As we have seen, states have invoked their “right” to “established”91 or “historic”92 uses of a watercourse, or have complained of pollution damage from uses upstream.93 The question here is to what extent such prior uses are protected by international law. There is a continuum of (p. 458) possibilities, ranging from absolute protection on one end to no protection at all, on the other.

These two extreme positions can be dispensed with immediately, on the basis of the earlier examination of their theoretical counterparts, absolute territorial integrity and absolute territorial sovereignty.94 That discussion showed that while these theories are sometimes invoked by states to defend their positions in specific disputes, they are virtually never the basis of the resolution of actual controversies. A claim that established or historic uses are entitled to absolute protection is also tantamount to an assertion that first in time is first in right. This idea is unsound as a matter of both policy and law. It encourages a “race to the river” and rewards the “winner” with absolute protection, regardless of the merits of either its use or the potential uses of other states, and regardless of the optimal utilization of the drainage basin as a whole.95 It condemns later-developing states—typically those upstream96—to permanent underdevelopment almost entirely because of the largely haphazard way in which political boundaries have carved up drainage basins.

Beyond being untenable on policy grounds, such a claim finds only scant support in the manner in which states have resolved actual controversies, as we have seen.97 It is true that protection of established uses is provided for in a number of treaties.98 This is, however, something quite different from asserting that there is a rule of general international law that absolutely protects such uses. States may always waive their rights by consent99—unless, of course, the right happens to be protected by a norm of jus cogens, which is highly unlikely in the field of international watercourses.100 But it is characteristic of these agreements that established uses of both states are protected, to their mutual advantage.

At the other end of the continuum, the idea that prior or established uses enjoy no protection at all finds its apotheosis in the “Harmon Doctrine” of absolute territorial (p. 459) sovereignty.101 As we saw in Chapter 4, this doctrine has not been followed—and indeed has been repudiated—by the state that originally articulated it. While today there are still occasional references to “sovereignty” by upstream states in relation to the law of international watercourses,102 it has been seen that there is no inconsistency between the notion of sovereignty and the idea that a state must respect the rights of other states in an international watercourse; they, too, have sovereign rights in respect of international watercourses. On the contrary, the rights of the other states, that are actually or potentially affected, are no less “sovereign” than those of the states asserting sovereign freedoms with regard to international watercourses. Moreover, the overwhelming majority of states reject the very idea of absolute territorial sovereignty with regard to international watercourses. The fact that no state defended it during the negotiation of the Watercourses Convention in the United Nations bears powerful witness to this proposition. And, as noted in Chapter 4, the anachronistic quality of the “absolute territorial sovereignty” theory is becoming ever more apparent as demand for finite water resources increases and the countries of the world become ever more interdependent.

Thus, established uses are not absolutely protected by international law but neither do they enjoy no protection at all.103 The protection to which they are entitled is determined by application of the principle of equitable and reasonable utilization. Procedurally, after a state demonstrates that it has suffered or might suffer significant harm to an existing use of an international watercourse, the burden of proof would shift to the state allegedly causing or threatening the harm to prove that its conduct or use of the watercourse was equitable and reasonable vis-à-vis the other state.104 The ensuing process is considered in the following section.

B.  Implementing the Principle of Equitable Utilization

In the case of the United States and some other federal systems, the equitable shares of the constituent units of the federation can be determined by the country’s highest court. As the U.S. Supreme Court explained in Kansas v Colorado:

whenever … the action of one State reaches through the agency of natural laws into the territory of another State, the question of the extent and the limitations of the rights of the two States becomes a matter of justiciable dispute between them, and this court is called upon to (p. 460) settle that dispute in such a way as will recognize the equal rights of both and at the same time establish justice between them.105

On the international plane there is, in the absence of acceptance by the states concerned, no court or tribunal with compulsory jurisdiction that can settle disputes between riparian states over rights in international watercourses. But the first stages of the procedure would be essentially the same as in a federal state: In the absence of an applicable agreement, each state must initially determine for itself whether its use of an international watercourse is equitable and reasonable vis-à-vis its co-riparian states. Completion of this step is necessary for each riparian to comply with its obligation of equitable and reasonable utilization. If one of those states believes another is not in compliance with its obligation of equitable and reasonable utilization, it will notify the other state to that effect. If the states disagree on the matter they will normally attempt to resolve their differences through negotiation.

What the tribunal in the Lake Lanoux case said about the obligations of a state contemplating a new use is relevant here:

Consideration must be given to all interests, whatever their nature, which may be affected by the works undertaken, even if they do not amount to a right . …

… The Tribunal considers that the upper riparian State, under the rules of good faith, has an obligation to take into consideration the various interests concerned, to seek to give them every satisfaction compatible with the pursuit of its own interests and to show that it has, in this matter, a real desire to reconcile the interests of the other riparian with its own.106

These same principles would apply whether the state planning a new use was upstream or downstream on the international watercourse.

Up to this point the same basic steps would generally be followed by both units of a federation and riparian countries. But if the parties are unable to resolve the dispute through negotiations, the paths followed on the national and international levels would diverge: while in many federations the dispute could be taken to the country’s highest court—a fact that might well encourage the parties to resolve the dispute through negotiation—there is generally no counterpart to this avenue for disputes between states, as already noted. They have at their disposal the normal means of dispute settlement, which range from negotiation to submission of the dispute to a third party, such as an arbitral tribunal or the ICJ.107 Most disputes concerning international watercourses are resolved through negotiations, which sometimes lead to the conclusion of a treaty.108 If a dispute cannot be so (p. 461) resolved, it may be submitted to arbitration—as France and Spain did in the Lake Lanoux case109—or to the ICJ—as, for example, Hungary and Slovakia did in the Gabčíkovo-Nagymaros case.110 Finally, while we have been assuming that there is no governing agreement, it should not be forgotten that many disputes over international watercourses are avoided because of the existence of joint commissions or other institutional mechanisms that have been established by treaties between the states concerned. In some instances, disputes have even been resolved by such mechanisms.111 And there is always the possibility that an agreement between the states concerned will include provision for compulsory settlement, as does the 1960 Indus Waters Treaty.112

It must be recognized that determination of a state’s equitable share is not, in many cases, a simple and straightforward matter. To be sure, extreme cases present few legal problems. For example, where downstream state A is the only one making use of a watercourse, upstream state B has no immediate cause for complaint; at this point A’s use could be said to be equitable and reasonable, although equity may require that A alter its use when and if B begins to make use of the watercourse. On the other hand, if we assume that state A has been using and relying upon the watercourse and state B begins diverting large quantities of water, leaving virtually none for A as a practical matter, B’s use would appear per se inequitable and unreasonable; some adjustments by both states would be required to bring the two states’ utilization of the river into balance. But between such extremes as these, one cannot pronounce a priori upon the equity or reasonableness of a state’s use of an international watercourse. All relevant factors must be taken into account in making this determination, and those factors, as well as their significance, will vary considerably from case to case.113 Indicative lists of such factors have been developed by national courts, as indicated above, and are given in both the Helsinki Rules114 and the UN Convention.115 However, these lists are neither exhaustive nor even necessarily fully relevant. Everything depends upon the unique characteristics of the case at hand.

(p. 462) C.  Equitable Utilization as a Process

More problematically for a state attempting to ensure that its own actual or potential use is equitable, many of the factors refer to information that cannot be obtained entirely within that state’s borders; much of it must be gathered from and provided by co-riparian states. Taking the UN Convention’s list of factors for purposes of illustration, information from co-riparians could be necessary for every single factor listed in Article 6, depending upon the position of the state on the watercourse, the nature of its actual or potential use, and the effect of that use on other riparian states.116 While this is bound to make accurate unilateral determinations of equitable utilization difficult at best, it is in the nature of the concept of equitable and reasonable utilization: it is the characteristics and uses of all relevant parts of the system, or drainage basin, that must be considered and assessed, not merely the situation in the assessing state’s own territory. To put it in terms of a simple metaphor, in order to determine whether its utilization is equitable and reasonable, a state must know what is happening on the other end of the balance—that is, in the other riparian state concerned. Moreover, equitable utilization is not an abstract and static state of affairs, but one that must be arrived at through an ongoing comparison of the situations and uses of the states concerned.

Obviously, then, for a state to ensure that its own use is equitable and reasonable, it must be provided with a variety of kinds of data and information by its co-riparians. And since what is equitable can change with changing circumstances, whether they be of natural or human origin,117 the information must be regularly updated. It is this kind of regular exchange of data and information between riparian states that is contemplated by Article 9 of the UN Convention.118 Without such information, the state will be forced to make what amounts to a blind assessment of the legitimacy of its use, a process that is not unlikely to result in a determination that is seen as inequitable and unreasonable by its co-riparians.

These considerations highlight the importance to equitable utilization of two-way communications between riparian states: such states not only need to receive information from other riparians, but must provide it to other riparians, as well. This is true not only of the kinds of data and information envisaged in Article 9 of the UN Convention, but also of information concerning changes in a state’s utilization of an international watercourse. As will be seen in Chapter 12, the principle of prior notification concerning new uses that may affect co-riparians appears now to be part of customary international law. A new use could throw a regime of equitable utilization out of balance and thus should be the subject of prior notification, consultation and, (p. 463) if need be, negotiation and possibly even third-party dispute settlement. Moreover, if—as seems to be the case—the obligation not to cause harm to co-riparians is an obligation of prevention,119 a state must exercise reasonable care—due diligence—to avoid engaging in activities that could result in such harm. Thus, both good faith fulfillment of the obligation of equitable utilization and the duty to prevent harm suggest that a state should not simply increase its utilization of a watercourse until another state cries foul. Rather, they imply that a state must: exercise due diligence to avoid depriving co-riparians of their equitable shares, as discussed in Chapter 10; and conduct a transboundary (environmental) impact assessment (TEIA) to determine whether a planned activity might have adverse impacts upon other riparian states,120 something that the ICJ has held is required by general international law,121 and, if the answer is in the affirmative, notify those other states thereof. Otherwise, the doctrine of equitable utilization would operate only as a post hoc check on a state’s use of the international watercourse in question. This is an approach to be avoided since once a new use is implemented it may quickly become entrenched and therefore difficult to alter. The preferable approach involves planning ex ante rather than dispute resolution ex post.

The obligation of equitable and reasonable utilization is thus best understood as a process. A state’s fulfillment of this obligation is dependent upon the regular receipt from other states of data and information concerning the watercourse, its provision of prior notification to other states of planned new uses that might affect them, and its conducting TEIAs to determine when activities in its territory might adversely affect other states’ utilization of the watercourse. The same is, of course, true of other states sharing the watercourse. The more intensively an international watercourse is utilized, the more scrupulous states will have to be in following these procedures. It therefore seems inescapable that implementation of the obligation of equitable and reasonable utilization depends ultimately upon good faith and ongoing cooperation between the states concerned. Experience suggests that such cooperation is most effective when it is institutionalized,122 a conclusion that would seem to be confirmed by the sheer number of international river commissions that have been established by co-riparian states.123 In fact, the doyen (p. 464) of all international organizations was the Central Commission of the Navigation of the Rhine.124 A highly effective and well-developed joint institutional mechanism (CARU) is provided for by the 1975 Statute of the River Uruguay, a treaty between Argentina and Uruguay,125 which was involved in the Pulp Mills case.126 The International Joint Commission between Canada and the United States, established by the 1909 Boundary Waters Treaty between the two countries,127 also fits this description.

The complexity of the process of attaining and maintaining an equitable allocation of shared water resources reinforces the proposition that equitable utilization is a principle of law, and not simply a matter of apportioning water ex aequo et bono, as Berber once thought.128 In his Individual Opinion in the Diversion of Water from the Meuse Case (Netherlands v Belgium), Judge Hudson wrote: “under Article 38 of the Statute, if not independently of that Article, the Court has some freedom to consider principles of equity as part of the international law which it must apply.”129

Equity is the lodestar in the apportionment of other shared natural resources as well, in particular fish stocks130 and the continental shelf.131 The ICJ’s use of equity in these fields establishes that the concept can inform rules of international law. In the Continental Shelf (Tunisia/Libya) case, the Court declared: “Equity as a legal concept is a direct emanation of the idea of justice . … [T]he legal concept of equity is a general principle directly applicable as law.”132 In the Fisheries Jurisdiction cases the Court stressed that the states in question had an obligation of reasonable use, the contours of which were to be determined through good faith negotiations aimed at reaching an equitable result. Specifically, the Court spoke of the “obligation to take account of the rights of other States and the needs of conservation.”133 It enjoined the parties “to conduct their negotiations on the basis that each must pay reasonable regard to the legal rights of the other …, thus bringing about an equitable apportionment of the fishing resources based on the facts of the particular situation.”134 If “water” were substituted for “fishing” in this sentence, the same thing could be said of the duties of riparian states. And with regard to maritime delimitation the (p. 465) Court has said: “The fundamental rule of general international law governing maritime delimitations … requires that the delimitation line be established while applying equitable criteria to that operation, with a view to reaching an equitable result . …”135

While speaking of other international problems, the important role of equity should also be noted in connection with efforts to protect the global environment, in particular in the prevention of stratospheric ozone depletion136 and global climate change,137 and the protection of biological diversity.138 The conventional regimes in these fields may be seen as implementing the principle of intragenerational equity—that is, equity as among those presently living on the planet.139


Equitable utilization is the fundamental rule governing the use of international watercourses. It is much more than a rule, however. It is a dynamic process, which depends heavily upon active cooperation between states sharing freshwater resources. A state’s regime of utilization that is equitable vis-à-vis its co-riparians today may not be next year. A new use in one state may change the equitable utilization calculus as among all riparians and therefore should be the subject of prior notification, consultation and, if necessary, negotiation. And, this is true whether the new use is made by an upstream or a downstream state: new upstream uses may have physical impacts upon those downstream; and new downstream uses may have legal impacts upon those upstream, because they may alter the equitable balance of uses in such a way as to make subsequent new uses in an upstream state inequitable. The need for close cooperation with regard to shared freshwater resources will only increase as global climate change continues to affect, for example, weather patterns, glaciers, which are melting ever more rapidly, and the precipitation in a given basin.

Achieving equity is not an exercise in unguided discretion, and an equitable result is a requirement of general international law. The use of equity is virtually compelled when natural resources that must be apportioned are shared by more than one state. This is especially true of flowing water, as to which “the action of one State reaches through the agency of natural laws into the territory of another State.”140 (p. 466) For not only are the waters of an international watercourse in constant motion along or across boundaries, they also constitute, in Justice Holmes’ words, “a necessity of life.”141 They therefore “must be rationed among those who have power over [them].”142 And in this rationing process “the effort always is to secure an equitable apportionment without quibbling over formulas.”143


1  See generally J. Bruhács, pp. 155, et seq. (Akadémiai Kiadó, Budapest, 1993); Caflisch, pp. 141, et seq.; Lipper; and McCaffrey, Second Report, pp. 103–33.

2  Kansas v Colorado, 206 U.S. 46 (1907). Important later cases include Wyoming v Colorado, 259 U.S. 419, modified, 260 U.S. 1 (1922), amended, 353 U.S. 953 (1957); Connecticut v Massachusetts, 282 U.S. 660 (1931); New Jersey v New York, 283 U.S. 336 (1931); Washington v Oregon, 297 U.S. 517 (1936); Colorado v Kansas, 320 U.S. 383 (1943); Nebraska v Wyoming, 325 U.S. 589 (1945), modified, 345 U.S. 981 (1953); Colorado v New Mexico, 459 U.S. 176 (1982); Texas v New Mexico, 462 U.S. 554 (1983); Colorado v New Mexico, 467 U.S. 310 (1984); and Kansas v Colorado, 475 U.S. 1079 (1986). Some of these cases, and others, are discussed in Griffin 1958. For a helpful review of these cases, see Sherk 1998.

3  See the early “Zwillikon Dam Case,” Aargau v Zurich, Entsch. des Schweizerischen Bundesgerichts (1878), vol. IV, p. 34, discussed in Smith at pp. 39–40, who characterizes it as “the earliest [case] … in which a judicial tribunal has approached the problem from the standpoint of international law,” ibid. p. 39; in Schindler, pp. 169–72; and in Griffin 1958, p. 76. See also, in particular, the Donauversinkung case, Württemberg and Prussia v Baden, 116 Entsch. des Reichsgerichts in Zivilsachen, app., p. 18 (1927), transl. in Ann. Digest of Pub. Int’l L. Cases, 1927–1928, vol. 4, p. 128 (1931), discussed in Ch. 5, above; and Province of La Pampa v Province of Mendoza, Supreme Court of Justice of Argentina, Dec. 1987, summarized in United Nations, International Rivers and Lakes Newsletter, No. 10, May, 1988, pp. 2–5.

4  Helsinki Rules on the Uses of the Waters of International Rivers, ILA, Report of the Fifty-Second Conference, Helsinki, 1966, p. 484.

5  1997 ICJ 7, Judgment of September 25, 1997, e.g., paras. 78, 85, 147, 150. In his dissenting opinion, Judge ad hoc Skubiszewski referred to it as the “canon of an equitable and reasonable utilization.” 1997 ICJ, p. 232, at p. 235, para. 8. See the discussion of this case in Ch. 6 section A.1.d.

6  ILC 1994 Rep., commentary to draft art. 7, at pp. 236, et seq.

7  See McCaffrey, Second Report, pp. 103–30, reviewing relevant treaties, positions taken by states in diplomatic exchanges, decisions of international courts and tribunals, other international instruments, the views of publicists, and decisions of municipal courts.

8  See, e.g., art. 5 of the UN Convention, according to which an international watercourse is to be utilized in an equitable and reasonable manner, “consistent with adequate protection of the watercourse.”

9  283 U.S. 336 (1931).

10  Ibid. at pp. 342–3.

11  These theories are discussed in Ch. 4.

12  Nebraska v Wyoming, 325 U.S. 589 (1945), modified, 345 U.S. 981 (1953).

13  This is particularly true where, as in this case, all the states involved follow the rule of priority of appropriation in their own territories. But the court observed that “if an allocation between appropriation States is to be just and equitable, strict adherence to the priority rule may not be possible.” Ibid, p. 618. Indeed, it has held that interstate allocation is governed by the federal doctrine of equitable apportionment, not state law. (Author’s footnote.)

14  Ibid. Two factors were proposed by Justice Douglas in his dissenting opinion in Arizona v California, 373 U.S. 546, at p. 627 (1963): the percentage of the area of a shared watercourse system within the respective states; and the extent to which a state diverted water out of the drainage basin. The Court, however, has never expressly considered these factors in its equitable apportionment decisions.

15  As discussed below, the U.S. Supreme Court rejected both priority and place of origin as determinative in Colorado v New Mexico, 459 U.S. 176 (1982). The Court considered that giving controlling weight to the latter factor would be “inconsistent with [its] emphasis on flexibility in equitable apportionment.” Ibid, p. 181, n. 8.

16  See, e.g., the Court’s recent decision in the third case between Kansas and Colorado concerning use of the Arkansas River, Kansas v Colorado, 514 U.S. 673 (1995), involving a contention by Colorado, the upper riparian, that it was being harmed by increased water use in Kansas.

17  Coase.

18  Compare Coase’s approach, according to which the objective is to avoid the more serious harm. Ibid.

19  See, e.g., Colorado v New Mexico, 459 U.S. 176 (1982) (concerning efficiency of water use and conservation measures in the downstream state); Colorado v New Mexico, 467 U.S. 310 (1984) (same); and New Jersey v New York, 283 U.S. 336, at p. 346 (1931) (requiring treatment of wastewater).

20  Colorado v New Mexico, 459 U.S. 176, 183 (1982).

21  206 U.S. 46 (1907).

22  Ibid, p. 117.

23  Ibid, p. 114.

24  Ibid.

25  Ibid, p. 117.

26  Ibid, p. 48.

27  Bourne 1965, p. 254. To the same effect, see Andrassy 1960, p. 34.

28  Kansas v Colorado, 206 U.S. 46 (1907), at p. 104, quoting from Elliott v Fitchburg Railroad Company, 10 Cush. 191, 193, 196, 64 Mass. 191 (1852).

29  See, e.g., Agenda 21, Chapter 18, part G, “Impacts of climate change on water resources,” paras. 18.82, et seq., Report of the United Nations Conference on Environment and Development, Rio de Janeiro, June 3–14, 1992, UN Doc. A/CONF.151/26/Rev.1 (Vol. I), p. 311 (1993); Goldenmann; Smerdon; Teclaff 1991; and The Colorado River Basin and the Greenhouse Effect.

30  See, e.g., the discussion of the importance of conservation and efficient use in the U.S. Supreme Court’s decisions in Colorado v New Mexico, 459 U.S. 176 (1982) and 467 U.S. 310 (1984).

31  Territorial Jurisdiction of the International Commission of the River Oder, Judgment No. 16, PCIJ, Ser. A, No. 23, p. 27.

32  Case concerning the Gabčíkovo-Nagymaros Project (Hungary/Slovakia), Judgment of September 25, 1997, 1997 ICJ 7, para. 85, p. 56.

33  Ibid, quoting from the River Oder judgment.

34  Kansas v Colorado, 206 U.S. 46, at p. 97 (1907).

35  Connecticut v Massachusetts, 282 U.S. 660, at pp. 670–1 (1931) (emphasis added).

36  Aargau v Zurich, Entsch. des Schweizerischen Bundesgerichts (1878), vol. IV, p. 34.

37  Ibid, pp. 46–7 (transl. from Schindler, p. 170).

38  Ibid, p. 47 (transl. from Schindler, p. 170).

39  21 Op. Att’y Gen. p. 280 (1895). See generally McCaffrey 1996.

40  1 Oppenheim 1905, p. 175.

41  Case concerning the Gabčíkovo-Nagymaros Project (Hungary/Slovakia), Judgment of September 25, 1997, 1997 ICJ 7, para. 78, p. 54.

42  This is not the place for an extended analysis of the meaning of the term “resource,” but its essential anthropocentrism should be recognized. The dictionary definition makes this plain: “1a: a source of supply or support: an available means …”; “b: a natural source of wealth or revenue …”; “c: a natural feature or phenomenon that enhances the quality of human life . …” Merriam-Webster Dictionary, available at <https://www.merriam-webster.com/dictionary/resource>.

43  The ICJ recognized the need to take environmental values into account in implementing a treaty project in the Gabčíkovo-Nagymaros case, ibid, paras. 112 and 146; and the Pulp Mills case, Pulp Mills on the River Uruguay (Argentina v. Uruguay), I.C.J. Reports 2010, p. 14, p. 83; as did the arbitral tribunal in the Kishenganga case, Indus Waters Kishenganga Arbitration (Pakistan v. India), Record of Proceedings (2010-2013), e.g., pp. 290–2, paras. 448–52, Permanent Court of Arbitration Award Series, Case No. 2011-01 (2014).

44  See generally Sherk 1989.

45  Dispute over the Status and Use of the Waters of the Silala (Chile v. Bolivia), information available at <http://www.icj-cij.org/en/case/162>.

46  Colorado v New Mexico, 459 U.S. 176, at p. 178 (1982).

47  Ibid.

48  These were Phelps Dodge Corp., Kaiser Steel Corp., Vermejo Park Corp., and the Vermejo Conservancy District.

49  Kaiser Steel Corp. v C.F. & I. Steel Corp., Civ. No. 76–244 (D.N.M. 1978).

50  Colorado v New Mexico, 459 U.S. 176, at p. 179 (1982).

51  Ibid, p. 180.

52  “An acre-foot is a volumetric measurement which means the amount of water required to cover one acre of ground one foot deep. One acre-foot equals 43,560 cubic feet or 325,900 gallons of water.” 459 U.S. p. 180, n. 5.

53  Report of the special master, as referred to in the Court’s opinion. 459 U.S. p. 180.

54  459 U.S. p. 181, referring to Report of the Special Master at p. 23 (footnotes omitted).

55  459 U.S. pp. 182–3.

56  459 U.S. p. 181, n. 8. The Court was prompted to reject any such per se rule of apportionment by New Mexico’s contention that the special master had relied on it in arriving at his decision. The Court stated that such a rule would be “inconsistent with our emphasis on flexibility in equitable apportionment.” Ibid.

57  459 U.S. p. 183, quoting from Nebraska v Wyoming, 325 U.S. 589, at p. 618 (1945). The Court set forth the factors listed in the latter case, which were quoted earlier.

58  459 U.S. p. 184, quoting from Wyoming v Colorado, 259 U.S. 419, at p. 484 (1922).

59  459 U.S. p. 184, quoting from Washington v Oregon, 297 U.S. 517, at p. 527 (1936).

60  459 U.S. p. 184.

61  Ibid, p. 185.

62  Ibid, p. 185, quoting from Wyoming v Colorado, 259 U.S. 419, at p. 484 (1922).

63  459 U.S. pp. 185–6, quoting from 259 U.S. at p. 484, note 11.

64  459 U.S. p. 186.

65  This was the Vermejo Conservancy District, which is the largest user of Vermejo water, consisting of “over 60 farms irrigated by an extensive system of canals and reservoirs.” 495 U.S. p. 181, n. 6. The special master found that the District “has never been an economically feasible operation.” 459 U.S. p. 181, quoting from the Report of the Special Master, at p. 23.

66  459 U.S. p. 190.

67  Ibid. p. 186.

68  Ibid. p. 187.

69  Ibid. This analysis could also be applicable in international cases, such as that involving Ethiopia’s construction of the Grand Ethiopian Renaissance Dam (GERD) and downstream Egypt’s protests that the dam would interfere with existing Egyptian uses. This situation is discussed in Ch. 7.

70  Ibid.

71  Ibid. p. 188.

72  Ibid.

73  Ibid. pp. 189–90.

74  467 U.S. 310, at p. 315 (1984).

75  Ibid. p. 316. Speaking of the decisions of the U.S. Supreme Court in interstate apportionment cases generally, one commentator has observed that where existing uses “have been established without objection of the other state or states, and were established as beneficial, the court has placed a great burden on the complaining state to prove their inequitableness.” Johnson 1959, p. 395. While the case cited as typifying support for this proposition involved an attempt by a downstream state to enjoin established uses in one upstream, the same principle would generally hold true in the more usual case where the existing uses were in the downstream state. Colorado v Kansas, 320 U.S. 383, 394 (1943). The latter case had actually originated with a complaint by Colorado, the upstream state, seeking to enjoin litigation by downstream water users in Kansas. Kansas then brought a cross bill to enjoin diversions in Colorado that allegedly interfered with existing uses in Kansas. The court refused to grant the injunction on the ground that Kansas had not carried its burden of showing that it was being harmed by the uses in Colorado.

76  467 U.S. 310, at p. 317 (1984).

77  Colorado v New Mexico, 467 U.S. 310, at pp. 317–23 (1984).

78  Ibid, p. 320, quoting from its earlier decision in the case, 459 U.S. at p. 186.

79  467 U.S. p. 320.

80  Ibid.

81  Ibid, p. 322.

82  Ibid. p. 323, quoting from the special master’s Additional Factual Findings at p. 29.

83  467 U.S. p. 323, citing 459 U.S. at p. 181, n. 8.

84  Ibid. While the Court was speaking of “equitable apportionment of appropriated rights,” ibid, the same principle applies to equitable apportionment in general.

85  467 U.S. p. 324. Justice Stevens wrote a strong dissent, arguing that the special master’s conclusion that reasonable conservation measures in New Mexico would offset the Colorado diversion was supported by the record. Ibid.

86  Ibid. It will be recalled that in its 1907 decision in Kansas v Colorado the Court had also assured Kansas that it could bring new proceedings if it appeared that increased diversions in Colorado were injuring interests of Kansas to the extent of upsetting the equitable apportionment of benefits between the two states. 206 U.S. 46, at p. 117.

87  Kansas v Colorado, 206 U.S. 46 (1907), discussed above.

88  See the UN Convention, Annex I, art. 7(2); and the Helsinki Rules, art. V(2)(j) and (k) and the commentary thereto.

89  UN Convention, ibid, art. 6(f). See also the Helsinki Rules, art. V(i).

90  See, e.g., the quotation from Andrassy’s Preliminary Report of the Ninth Commission of the Institut de Droit International in n. 103, below. On the problem of existing uses, see generally Johnson 1959; Goldie, p. 399; Bruhács, pp. 132, et seq.; Caflisch, pp. 158–60; and Fuentes, pp. 356, et seq.

91  Egypt has taken this position with respect to the Nile. See Ch. 7, section A. See also Godana, p. 39.

92  This position was taken by Mexico in the controversy over the Rio Grande leading to the articulation by the United States of the Harmon Doctrine. See, e.g., Minister Romero to U.S. Secretary of State Richard Olney, October 21, 1895, in 22 U.S. Appendix, pp. 200, 202. Egypt has also taken this position vis-à-vis Sudan. See Exchange of Notes between the United Kingdom [acting for Sudan] and Egypt in regard to the Use of the Waters of the River Nile for Irrigation Purposes, May 7, 1929, No. 1, para. 2, Legislative Texts, p. 100, Treaty no. 7. See generally Chs. 3 and 7.

93  A well-known example is the long-running controversy between France and the Netherlands resulting from chloride pollution of the Rhine by the French Mines de Potasse d’Alsace. See the discussion of this case in Ch. 7 section C.1.

94  See Ch. 4, sections B and A, respectively.

95  See, e.g., the discussion in Dellapenna, pp. 248–9, of the relative wealth of Egypt, Sudan, and Ethiopia (the first two being relatively more wealthy than the third) and the impact of according priority to the existing uses in Egypt and Sudan.

96  Downstream countries are usually flatter, and thus better suited to agriculture; upstream countries, generally being more mountainous, had few ways in which to develop their water resources before the advent of large dams and hydroelectric power. One need only consider the cases of the Nile and the Euphrates for illustrations of this proposition. The same phenomenon is occurring today on the Mekong and on rivers flowing from Nepal into India. See generally Ch. 7.

97  See the cases and controversies reviewed in Chs. 6 and 7. Perhaps the most outstanding exception, or apparent exception, is Egypt on the Nile. However, now that Ethiopia is in a somewhat better geopolitical position to develop the Blue Nile, and has actually done so, strikingly, in the form of the Grand Ethiopian Renaissance Dam, it appears that Egypt is showing some flexibility. See the discussion in Ch. 7; and Dellapenna, p. 247.

98  See, e.g., the agreements reviewed by Bruhács, pp. 134–5.

99  See art. 29 of the International Law Commission’s draft articles on State Responsibility, 1996 Y.B. Int’l L. Comm’n, vol. 2, pt. 2, p. 61.

100  The suggestion by Hayton that the doctrine of “equality of right” to the beneficial uses of an international watercourse enjoys the status of a peremptory norm seems doubtful. Hayton 1967a, pp. 835–6. If the idea is that the sovereign equality of states constitutes a peremptory norm, the Permanent Court, as early as 1923, affirmed that the incurring of treaty obligations was an expression, rather than an abandonment, of sovereignty. The Wimbledon, PCIJ, Ser. A, no. 1, p. 25.

101  Clearly, the idea can also cover an established upstream use that is interfered with, factually or by changing the legal regime, by a new use downstream. This has been recognized by the U.S. Supreme Court in its interstate apportionment decisions, as has been seen.

102  This was the attitude of, e.g., China, with regard to the UN Convention. See the statements of the Chinese delegate, Gao Feng, reported by the Xinhua News Agency on May 21, 1997.

103  According to Andrassy’s Preliminary Report of the Ninth Commission of the Institut de Droit International on “Utilization of Non-Maritime International Waters (Apart from Navigation): “The members of the Commission are in general of the opinion that these [i.e., existing uses] must be respected, but not in an absolute manner.” Ibid, p. 42 (Geneva, July, 1959).

104  See the ILC’s commentary to its draft article 7, ILC 1994 Report, para. 14, at pp. 241–2. See also Lester 1967, p. 113.

105  206 U.S. at pp. 97–8. It should be noted, however, that exercise of original jurisdiction by the U.S. Supreme Court in disputes between states is discretionary; it is not a matter of right. See, e.g., Nebraska v Wyoming, 115 S.Ct. 1933, at p. 1938 (1995); and Mississippi v Louisiana, 113 S.Ct. 549, at pp. 552–3 (1992).

106  12 UNRIAA p. 281, at p. 315. English translations in [1974] Y.B. Int’l L. Comm’n, vol. 2, pt. 2, p. 198; and 53 AJIL 156 (1959).

107  See the well-known catalogue of procedures contained in art. 33 of the United Nations Charter. Dispute resolution is discussed in Ch. 14; and in McCaffrey, Sixth Report, part IV, pp. 66–80.

108  See, e.g., the discussion in Art 4 of the 1906 treaty between Mexico and the United States, Legislative Texts, Treaty No. 75, p. 232, which resolved the dispute over the Rio Grande that had produced the Harmon Doctrine; the 1960 Indus Waters Treaty between India and Pakistan, 419 UNTS 126, Legislative Texts, Treaty No. 98, p. 300, resolving a long-running dispute between those two countries; and the Treaty relating to Cooperative Development of the Water Resources of the Columbia River Basin of January 17, 1961 between Canada and the United States, 15 UST 1555, 542 UNTS 244, Legislative Texts, Treaty No. 65, p. 206, which settled a dispute over the use of that river.

109  12 UNRIAA p. 281. English translations in [1974] Y.B. Int’l L. Comm’n, vol. 2, pt. 2, p. 198; and 53 AJIL p. 156 (1959). See also the other arbitral awards discussed in Ch. 6 section A.2.

110  1997 ICJ 7. See also the other judicial decisions discussed in Ch. 6 section A.1.

111  Two examples may be drawn from the practice of the International Joint Commission between Canada and the United States, established by the 1909 Boundary Waters Treaty between the two countries, 36 U.S. Stat. 2448, U.S. Treaty Series 548: the High Ross Dam case and the Garrison Diversion case. On the former, see Parker. On the latter, see International Joint Commission, Report to the Governments of Canada and the United States on Transboundary Implications of the Garrison Diversion Unit (1977).

112  1960 Indus Waters Treaty between India and Pakistan, 419 UNTS 126, art. IX(5).

113  See Fuentes, attempting to assess the potential relevance of the various factors. See also Nebraska v Wyoming, 325 U.S. 589, at p. 618 (1953).

114  Annex II, art. V.

115  Annex I, art. 6.

116  It is also true of every international and national decision referred to in this section that information from other riparian states was needed to determine the propriety of the use of the state in question.

117  For example, less than normal precipitation in a state situated in the upper portion of a drainage basin will affect the quantity and perhaps also the quality of water available in states downstream. The same is true of the initiation of a large irrigation project by a state in the basin.

118  Annex I. Art. 9, contained in Part II of the Convention, General Principles, is entitled “Regular exchange of data and information.”

119  See art. 7(1) of the UN Convention, Annex I. This point will be discussed further in the following chapter. The relationship between the obligation of equitable utilization and the duty not to cause harm to other riparian states is considered in the following chapter.

120  Art. 12 of the UN Convention provides that notification of prospective uses is to be accompanied by “the results of any environmental impact assessment.” Such an assessment is required by the Helsinki Convention on the Protection and Use of Transboundary Watercourses and International Lakes, March 17, 1992, art. 3(1)(h), 31 ILM 1312 (1992). See generally the Espoo Convention on Environmental Impact Assessment in a Transboundary Context, February 25, 1991, 30 ILM 800 (1991). Both are ECE conventions.

121  Pulp Mills on the River Uruguay (Argentina v. Uruguay), ICJ Reports 2010, p. 14, p. 83, para. 204.

122  See, e.g., International River and Lake Basins. The delegations negotiating the UN Convention thought joint institutions so important that they added a paragraph to art. 8, General obligation to cooperate, that suggests states “consider the establishment of” such organizations to realize and facilitate cooperation on relevant measures and procedures.

123  A survey of multipartite and bipartite commissions concerned with non-navigational uses of international watercourses compiled by the United Nations Secretariat in 1979 lists 90 such bodies. Annotated list of multipartite and bipartite commissions concerned with non-navigational uses of international watercourses, April, 1979 (mimeo). This seems understated today. See generally McCaffrey 1998.

124  Reuter, p. 207. On the Central Commission see, e.g., Kaeckenbeeck, p. 34, et seq.

125  1295 UNTS p. 340.

126  Pulp Mills, note 121 above.

127  January 11, 1909, 102 BFSP p. 137; Legislative Texts, Treaty No. 79, p. 260.

128  Berber pp. 176–7. But Berber seems to have retracted this position when he lent his support to the Helsinki Rules. See Caflisch, p. 153.

129  PCIJ Reports, Ser. A/B, No. 70, pp. 76–7 (1937).

130  See the Fisheries Jurisdiction cases (U.K. v Iceland; F.R.G. v Iceland), 1974 ICJ pp. 3 and 175 (judgments of July 25, 1974), at p. 116.

131  See, e.g., the case concerning the Continental Shelf (Tunisia/Libyan Arab Jamahiriya), 1982 ICJ p. 18, where the ICJ stated that “the delimitation is to be effected in accordance with equitable principles, and taking account of all relevant circumstances; . …” Ibid, p. 92. See also Delimitation of the Maritime Boundary in the Gulf of Maine Area (Canada/United States of America), 1984 ICJ p. 246.

132  Continental Shelf (Tunisia/Libyan Arab Jamahiriya), 1982 ICJ p. 60, para. 71.

133  1974 ICJ p. 31, para. 71.

134  Ibid, p. 33, para. 78.

135  Gulf of Maine case, 1984 ICJ at p. 339.

136  Montreal Protocol on Substances that Deplete the Ozone Layer, September 16, 1987, 26 ILM 1550 (1987).

137  UN Framework Convention on Climate Change, May 9, 1992, 31 ILM 849 (1992).

138  UN Convention on Biological Diversity, June 5, 1992, 31 ILM 818 (1992).

139  This may be seen in the differential treatment accorded by these instruments to developed and developing countries, respectively, in view of the different contributions each has made to the problem in question. See generally Brown Weiss.

140  Kansas v Colorado, 206 U.S. 46, at p. 97 (1906).

141  New Jersey v New York, 283 U.S. 336, at p. 342 (1931).

142  Ibid.

143  Ibid. p. 343.