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10 needed water.

Of course, it is not surprising that a treaty ratified in 1868 did not envision and provide for all of the Navajos’ current water needs 155 years later, in 2023. Under the Constitution’s separation of powers, Congress and the President may update the law to meet modern policy priorities and needs. To that end, Congress may enact—and often has enacted—legislation to address the modern water needs of Americans, including the Navajos, in the West. Indeed, Congress has authorized billions of dollars for water infrastructure for the Navajos. See, e.g., Tr. of Oral Arg. 5, 11; Consolidated Appropriations Act, 2021, Pub. L. 116–260, 134 Stat. 3230.

But it is not the Judiciary’s role to update the law. And on this issue, it is particularly important that federal courts not do so. Allocating water in the arid regions of the American West is often a zero-sum situation. See Brief for Western Water Users and Trade Associations as Amici Curiae 13–14, 18–21. And the zero-sum reality of water in the West underscores that courts must stay in their proper constitutional lane and interpret the law (here, the treaty) according to its text and history, leaving to Congress and the President the responsibility to enact appropriations laws and to otherwise update federal law as they see fit in light of the competing contemporary needs for water.

The Navajo Tribe advances several other arguments in support of its claim that the 1868 treaty requires the United States to take affirmative steps to secure water for the