LAS VEGAS (KLAS) — A lawsuit by the parched Navajo Nation threatens to cloud the “who gets what” questions surrounding Colorado River water. U.S. Supreme Court justices heard arguments in the case Monday morning in Washington D.C.

And while the U.S. government acknowledged a “moral and political” need to ensure the Navajo people get water for domestic needs, lawyer Frederick Liu challenged whether the U.S. has a legal “duty” to pipe water in from the Colorado River.

Liu said the U.S. government has no duty to “construct pipelines, pumps or wells” to provide water to the Navajo Nation. They simply “can’t interfere” with the water rights that are clearly held by the Navajo Nation.

A lawyer for the Navajo Nation said the average person on the reservation uses about seven gallons a day, compared to the 80 gallons used by the average American.

Questions asked by the justices indicated some support for the Navajo Nation’s claim, which argues the U.S. has a duty to provide the necessary water for the reservation. One analysis of the hearing suggests that the appeal of the 2021 9th Circuit Court ruling could hinge on the vote of conservative Justice Amy Coney Barrett.

And Justice Brett M. Kavanaugh suggested it’s really more of a political issue that should be decided by Congress.

While the original lawsuit did not expressly seek water from the Colorado River, states are concerned that additional water for the tribe would disrupt current distribution, which is bound by the century-old “Law of the River.”

That’s because the treaty with the Navajo Nation predates that agreement, since the reservation was established by an 1868 treaty with the United States.

“Throughout the 20 years of litigation on this case, there’s only been one source of water identified. That’s the Lower Colorado River,” Rita Maguire said in arguing the case on behalf of Arizona.

The Navajo Nation alleges that the U.S. government has violated its trust by failing to secure water for the reservation — and, in fact, has stood in the way of the people negotiating their own solutions.

But Liu argued that the 1868 treaty really only addressed water for agriculture — not domestic use, which could be available from groundwater in the reservation.

Justices questioned whether the U.S. was living up to its end of the 1868 treaty, which created a permanent home for Navajos after they had been forced off the land once before. Justice Sonia Sotomayor challenged whether any “permanent home” could exist without sufficient water.

Justice Samuel A. Alito, Jr., pointed out that the reservation didn’t originally border the Colorado River, and Liu said the Little Colorado River had been the primary source of the reservation’s water when in 1868.