Julie Jacobson, AP
FILE - This March 23, 2012 file photo shows pipes extending into Lake Mead well above the high water mark, in Boulder City, Nev. Tribal leaders from four states gather in Las Vegas on Wednesday May 23, 2012, to issue a joint statement asking the Bureau of Land Management to deny the Southern Nevada Water Authority's proposed groundwater pipeline project application aimed at pumping billions of gallons of water from rural areas along the Nevada-Utah line to supplement Las Vegas' limited supply from Lake Mead.

LAS VEGAS — The Nevada Supreme Court rejected a Mormon church appeal Thursday on a narrow legal question in a broad water rights dispute surrounding a proposal to pump groundwater from arid valleys along the Nevada-Utah border and pipe it to Las Vegas.

The court unanimously denied a Church of Jesus Christ of Latter-day Saints contention that Nevada's top water official, state Engineer Jason King, misinterpreted state law when he decided in March 2012 to allow "incremental development" of pumping operations in the Spring Valley area.

"This is a matter of great public importance," the high court said, acknowledging that it was focusing on one question brought by the church while "hundreds of parties" contest the approvals received by Southern Nevada Water Authority for what the justices said was an effort "to help secure adequate water for this state's most populous region."

The court said King didn't retroactively apply a state law that allows pumping operations to begin in monitored increments.

Attorney Paul Hejmanowski, representing the church and its sprawling Cleveland Ranch in Nevada's White Pine County, said the ruling didn't cripple his case. He said he only wanted to clarify rules for hearings yet to come before King.

"Our case will go back before the engineer on approval," Hejmanowski said. "This was about how he interprets a particular statute."

"If I were right, and the engineer went through the whole proceeding again and it had an error, it would come right back again," the attorney added.

King called the court ruling "what we expected."

Water authority spokesman Scott Huntley said confirming King's authority to let groundwater pumping in Spring Valley begin in stages and increase over time would show critics that "the sorts of environmental harms and water use conflicts hypothesized by project opponents will not occur."

The water authority owns land and water rights in the valleys, but hasn't allocated funds for the pipeline. It would stretch a distance farther than from New York City to Washington, D.C. Cost estimates are in the billions of dollars.

The state Supreme Court last year let stand a December 2013 order by a judge in Ely that King recalculate the amount of water available and establish standards for limiting possible environmental damage in White Pine and Lincoln counties.

Pressure to find other sources for water for Las Vegas has increased in recent years amid ongoing record drought in the Southwest and the depletion of the Lake Mead reservoir behind Hoover Dam on the Colorado River to less than half full. Las Vegas, with its 2 million residents and 40 million visitors a year, currently draws about 90 percent of its drinking water from Lake Mead.

King's ruling in March 2012 granted the water authority permission to pump up to 84,000 acre-feet of water a year from the Spring Valley, Cave, Dry Lake and Delamar valleys. That would increase the available water supply to Las Vegas by almost 30 percent. Water officials in Las Vegas say one acre-foot, or 326,000 gallons, can serve two households for a year.

Environmental groups in Nevada and Utah say the pumping would ruin fragile ecosystems and turn the valleys to dust bowls.