Las Vegas - Government leaders in the United States and Mexico are close to signing a pact to add areas south of the border to Colorado River water sharing agreements involving seven Western US states, officials said.

US Bureau of Reclamation officials characterized the talks as delicate while final documents circulate among 15 water agencies and state officials in Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming.

"The concern is that these are sensitive negotiations," said Kip White, a bureau spokesman in Washington, D.C. "It has taken a long time to get here. We're looking forward to a culmination of this later this month."

"It's not a completed agreement until the document is signed," added Rose Davis, a bureau spokeswoman in Boulder City.

The framework of the five-year agreement became public with agenda items for a meeting this week in Las Vegas involving the Southern Nevada Water Authority and Colorado River Commission of Nevada. The Las Vegas Review-Journal first reported it last Friday.

The pact is an addendum to a 1944 US-Mexico water treaty.

It developed from talks begun when the seven Colorado River states signed a landmark agreement in 2007 to share the pain of shortages and the wealth of surpluses from the Colorado River reservoirs of Lake Mead and Lake Powell. The water users called at the time for federal officials to get Mexico to participate.

The agreement would also link Mexican and US water allocations from the Colorado River during surplus and drought. The documents never refer to shortage, but instead cite "low reservoir conditions."

"Provisions include Mexico agreeing to adjust its delivery schedule during low reservoir conditions, Mexico having access to additional water during high reservoir conditions, and a commitment to work together on a pilot program that includes water for the environment," according to a summary submitted to voting SNWA and Colorado River Commission members.

The agreement would let Mexico continue an emergency program begun two years ago to store water in Lake Mead, the reservoir behind Hoover Dam near Las Vegas.

After pipelines and canals were damaged by a magnitude 7.2 Easter Sunday 2010 earthquake, Mexico asked the US at the time to let it store water temporarily while repairs were made to irrigation systems in a broad agricultural area south of Mexicali. The area is irrigated by water from the Morelos Dam on the Colorado River west of Yuma, Arizona.

The agreement also calls for a pilot program of water releases from the US to replenish wetlands in the Colorado River delta of the Gulf of California, and it clears the way for the US government and municipal water agencies to invest in infrastructure improvements in Mexico in return for a share of the water such projects would save.

Las Vegas gets 90 percent of its drinking water from drought-stricken Lake Mead, and officials have talked about paying to build a seawater desalination plant in Mexico to trade for additional water rights to Colorado River water.

The Review-Journal reported that the two largest municipal water agencies in Arizona and California have signed off on the agreement.

New Mexico's Interstate Stream Commission is due to consider the agreements next week.

Jeff Kightlinger, general manager of the Metropolitan Water District of Southern California, said his board has approved the agreement.

The agreement calls for the Southern California district to pay Mexico $5 million over three years in return for 47,500 acre-feet of water. The agencies in Arizona and Nevada would each pay $2.5 million over three years and receive a total of 23,750 acre-feet.

An acre-foot of water is about enough to serve two Las Vegas-area households for a year, officials say.