Las Vegas Wash, in the distance, empties into Lake Mead on Friday afternoon. Nevada already receives credits for any Colorado River water used in the Las Vegas Valley and returned to the lake in the form of treated wastewater released into the wash. Under a concept approved Friday, the state also would get similar credits for the groundwater it plans to pipe to Las Vegas from rural Nevada. Photo by Ralph Fountain.

Nevada won key concessions that should provide more water to a thirsty Clark County, as two days of closed-door talks on the future of the Colorado River wrapped up on Friday at Lake Las Vegas.

It's too soon to say how much more water the state might get, but Southern Nevada Water Authority General Manager Pat Mulroy said concepts approved during the talks represent "everything we needed from the Colorado River."

The purpose of the meeting was for the seven states that share the Colorado River to come to some consensus on how to divide the resource and operate the twin reservoirs of Lake Mead and Lake Powell when supplies are low.

On the way to a tentative agreement on those issues, the states gave Nevada permission to collect so-called augmentation credits for any of the state's groundwater that is used in the Las Vegas Valley and released into Lake Mead as treated wastewater.

Depending on how the new credit system works, it could allow the water authority to almost double the number of people it can serve with the groundwater it plans to pipe in from rural parts of the state.

Water managers also agreed to let Nevada supplement its river allocation with additional water the state could make available through what Mulroy called "efficiency improvements" on the Colorado.

Bob Johnson, director of the Bureau of Reclamation's Lower Colorado Region, said one such improvement involves the construction of a new reservoir just north of the U.S.-Mexico border to store surplus water that would otherwise flow into Mexico but not count against that country's river allocation.

"I'm not saying that's going to happen. That's just an example," Johnson said.

In exchange for the water Nevada would gain through efficiency improvements, Mulroy said the water authority has agreed to temporarily suspend its plans to divert water to Las Vegas from the Virgin and Muddy rivers.

Some feared that project could land the basin states in court by stoking a long-simmering dispute over the use of tributary water.

Mulroy said the sometimes-tense interstate negotiations began at 10 a.m. Thursday and lasted until 9:30 p.m. Attorneys for some of the groups continued to meet until midnight.

The discussions ended about noon Friday with an agreement to return to Las Vegas on Jan. 30 so the seven states can finalize the consensus plan they will deliver to Interior Secretary Gale Norton next month.

That will be "another all-day-and-into-the-night meeting," Mulroy said.

Until then, water managers and their technical staffs will work to turn their concepts into workable, real-world plans.

"The devil's always in the details," Mulroy said.

So far, those details are in short supply. Mulroy said water managers are being especially tight-lipped because some of the ideas discussed could be controversial, and "they've got to go home and sell them."

Some key issues remain up in the air.

For example, Johnson said the states have agreed to a concept under which shortages of various sizes would be declared in the lower basin when the water level in Lake Mead falls below a certain point. The size of those shortages and what lake elevations would trigger them is yet to be determined.

"The recommendation we are looking for really requires a lot more detail," Johnson said.

Norton wants to be able to announce shortage criteria and a new reservoir-operating scheme for the Colorado River by the end of 2007. To do that, she gave the basin states until February to develop their consensus plan so it can undergo federal environmental review.

Based on the progress made this week, Mulroy said she is "hugely confident" the states will meet Norton's deadline.

"This meeting was a huge success," said Mulroy, who is the state's lead negotiator on Colorado River issues. "What we have is agreements in concept on all the issues."

Johnson was also encouraged by what he saw at the meeting.

"I do sense a positive attitude on all of their parts, and that hasn't always been there," he said. "I think there's reason for optimism."