concurring in the judgment.
The doctrine of prior appropriation includes the requirement that the appropriator’s use of water be beneficial and reasonable. What is reasonable, of course, does not admit of ready definition, being dependent upon the particular facts and circumstances of each case. In this case, the Special Master has cast an accusatory finger at the Vermejo Conservancy District, concluding that “[t]he system of canals used to transport the water to the fields is inefficient.” Report of Special Master 8.
Undoubtedly, there is evidence in the record indicating that large losses of water occur through seepage and evaporation in transporting waters of the Vermejo through open *192ditches for irrigation and stock watering. Tr. 1315. It is a leap, however, from observing that large losses occur to concluding, as Colorado would have the Court do, that the practices of the Conservancy District are wasteful or unreasonable. As the Court observes, ante, at 185, the extent of the duty to conserve that may be placed upon the user is limited to measures that are “financially and physically feasible,” Wyoming v. Colorado, 259 U. S. 419, 484 (1922), and “within practicable limits.” Ibid.1 Nevertheless, in concluding that the Conservancy District’s distribution system is “inefficient,” the Special Master made no factual finding that improved economy in that system is within the practicable means available to the District.2
Colorado would have the Court assess the Conservancy District’s “waste” and “inefficiency” by a new yardstick— i. e., not by comparing the economic gains to the District with the costs of achieving greater efficiency, but by comparing the “inefficiency” of New Mexico’s uses with the relative benefits to Colorado of a new use. The Special Master has succumbed to this suggestion. His recommendation that *193Colorado be permitted a diversion embodies the judgment that, because Colorado can, in some unidentified sense, make “better” use of the waters of the Vermejo, New Mexico may be forced to change its present uses.
Today the Court has also gone dangerously far toward accepting that suggestion. The Court holds, ante, at 186, that it is appropriate in equitable apportionment litigation to weigh the harms and benefits to the competing States. It does so notwithstanding its recognition, ante, at 187, that the potential benefits from a proposed diversion are likely to be speculative and remote, and therefore difficult to balance against any threatened harms, and its concession, ibid., that the equities supporting protection of an existing economy will usually be compelling.
In equitable apportionment litigation between two prior appropriation States concerning the waters of a fully appropriated river, this Court has never undertaken that balancing task outside the concrete context of either two established economies in the competing States dependent upon the waters to be apportioned3 or of a proposed diversion in one State to satisfy a demonstrable need for a potable supply of drinking water.4 In the former context, the Court may assess the relative benefit and detriment by reference to the *194actual fruits of use of the waters in the respective States.5 In the latter context, the compelling nature of the proposed use reduces the speculation that might otherwise attend assessment of the benefits of a proposed diversion. Where, as here, however, no existing economy in Colorado depends on *195the waters of the Vermejo and the actual uses in New Mexico rank in equal importance with the proposed uses in Colorado,6 the difficulty of arriving at the proper balance is especially great.
This case therefore highlights the restraint with which the Court should proceed in apportioning interstate waters between a State seeking a future use and a State with an existing economy dependent upon the waters to be apportioned. The Court can only invite litigation within its original jurisdiction if it permits one State to obtain a diversion for a new use upon that State’s allegation that the second State is engaging in “wasteful” practices or that it can make “better” use of the waters, even if the second State’s uses are entirely reasonable.
I do not suggest, of course, that the Court must blind itself to compelling evidence of waste by one State. Protection of existing economies does not require that users be permitted to continue in unreasonably wasteful or inefficient practices. But the Court should be moved to exercise its original jurisdiction to alter the status quo between States only where there is clear and convincing evidence, ante, at 188, n. 13, that one State’s use is unreasonably wasteful. To allow Colorado a diversion upon a lesser showing comports neither with the equality of rights of the litigants before us, see Connecticut v. Massachusetts, 282 U. S. 660, 670 (1931), nor with the sparing use that should be made of the Court’s equitable powers, see id., at 669. Further, such action would seriously undermine the Court’s affirmation, ante, at 184, that priority of appropriation is the “guiding principle” in allocating waters between two prior appropriation States.
The Court’s remand reflects its judgment that the paucity of the factual findings before us furnishes an inadequate basis *196upon which to make “the delicate adjustment of interests” at stake, Nebraska v. Wyoming, 325 U. S. 589, 618 (1945). I concur in that disposition insofar as the Special Master’s findings and conclusions do not provide a basis for determining whether Colorado has demonstrated by clear and convincing evidence that the Conservancy District has engaged in unreasonably wasteful practices.
It is significant to note that in Wyoming v. Colorado, upon which the Court relies for the proposition that an affirmative duty to conserve may be imposed on the States, ante, at 185, the Wyoming appropriators already had storage facilities in place for equalizing the river’s natural flow. In answering Wyoming’s objection that it should not be burdened with conservation measures in order to permit a diversion by Colorado, the Court observed:
“We think [the] doctrine [of appropriation] lays on each of these States a duty to exercise her right reasonably and in a manner calculated to conserve the common supply. Notwithstanding her present contention, Wyoming has in fact proceeded on this line, for, as the proof shows, her appropriators, with her sanction, have provided, and have in service reservoir facilities which are adapted for the purpose and reasonably sufficient to meet its requirements.” 259 U. S., at 484-485 (emphasis added).
Evidence in the record indicates that the Conservancy District has employed an engineering firm to investigate the feasibility of constructing an enclosed system to deliver stock water to the District’s landowners. Tr. 1318.
See Nebraska v. Wyoming, 325 U. S. 589 (1945); Washington v. Oregon, 297 U. S. 517 (1936); Kansas v. Colorado, 206 U. S. 46 (1907).
See New Jersey v. New York, 283 U. S. 336 (1931); Connecticut v. Massachusetts, 282 U. S. 660 (1931). It is also significant to note that these disputes occurred between two riparian States.
Wyoming v. Colorado, supra, does not represent an exception to the pattern stated in the text. The Court did not engage in any wholesale balancing of the relative harms and benefits to the two States from the proposed diversion. Rather, the Court imposed a very limited duty on Wyoming to make use of the storage facilities its appropriators already had in place, see n. 1, supra, for the purpose of calculating the dependable supply of water available to Wyoming. 259 U. S., at 484. The Court was thereby able to determine that the waters of the Laramie River were not fully appropriated and that a share of the waters was available for Colorado’s proposed use.
For example, in Kansas v. Colorado, supra, Kansas sought to restrain Colorado from diverting waters of the Arkansas River for the irrigation of lands in Colorado. Colorado had diverted waters from the river since the 1880’s. As a result of irrigation, the population of the irrigated areas, the number of acres cultivated, and the value of farm products produced in these areas escalated dramatically. 206 U. S., at 108-109. The Court compared this demonstrated salutary effect of the irrigation on the economy of Colorado with the corresponding population changes and changes in acreage and production of com and wheat in the affected Kansas counties for the same period. Id., at 110-118. Using these concrete data, the Court was able to discern some minimal injury to Kansas as a result of the diminution of the flow of the Arkansas River. Id., at 113-114. Viewing the overall impact of the available water on the two economies, however, the Court concluded:
“[W]hen we compare the amount of this detriment [to Kansas] with the great benefit which has obviously resulted to the counties in Colorado, it would seem 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.” Ibid.
Quite clearly, the Court was not forced to speculate about the benefit and detriment of the diversion to the competing States.
Similarly, in Washington v. Oregon, supra, the Court was equipped to assess the balance of harm and benefit to the economies from the diversion at issue. Washington sought an injunction against Oregon’s diversion of waters of the Walla Walla River for irrigation in Oregon. On the one hand, Oregon had an existing agricultural economy dependent upon irrigation from the Walla Walla. On the other hand, the evidence revealed that there would be absolutely no benefit to Washington in prohibiting Oregon’s diversion during periods of water shortage; the nature of the river channel was such that even if the water was not diverted by Oregon users, it would be absorbed by the gravel beneath the channel and never reach Washington users. 297 U. S., at 522-523. The Court therefore concluded that “[t]o limit the long established use in Oregon would materially injure Oregon users without a compensating benefit to Washington users.” Id., at 523.
According to Colorado, the diverted water would be used “in industrial operations at coal mines, agriculture, timbering, power generation, domestic needs and other industrial operations . . . .” Reply Brief for Colorado 8.