LAS VEGAS — Government officials from United States and Mexico have made a Tuesday date in San Diego to sign a landmark agreement to share Colorado River water during times of drought and surplus.The time and place were confirmed Friday by International Boundary and Water Commission official Gustavo Ramirez. The commission’s U.S. section secretary, Sally Spener, said this week from El Paso, Texas, that there were still a number of reviews and approvals needed north and south of the border before the addendum to a 1944 U.S.-Mexico water treaty is signed.The Southern Nevada Water Authority and Colorado River Commission of Nevada unanimously approved the pact Thursday, authority spokesman Scott Huntley said.The two entities, along with the Metropolitan Water District of Southern California and the Central Arizona Project, are among the largest of the 15 agencies and state officials in Arizona, California, Colorado, Nevada, New Mexico, Utah and Wyoming whose approvals are needed, along with representatives of Mexico and the U.S. Bureau of Reclamation.New Mexico’s Interstate Stream Commission unanimously approved the agreement Wednesday.The Bureau of Reclamation manages Colorado River reservoirs in the U.S. including Lake Mead behind Hoover Dam and Lake Powell behind Glen Canyon Dam near Page, Ariz. Lake Mead is the primary drinking water supply for Las Vegas.The five-year agreement developed from talks begun before the seven Colorado River states signed a landmark agreement in 2007 to share the pain of shortages during drought and surpluses during wet years. The river runs some 1,450 miles from the Rocky Mountains of Colorado to the Gulf of California.The agreement calls for letting Mexico store water in Lake Mead, and for a pilot program of water releases from the U.S. to replenish wetlands in the Colorado River delta south of the border.The water agencies in California, Arizona and Nevada would each buy water from Mexico over three years. The agreement also clears the way for U.S. entities to invest in infrastructure improvements in Mexico in return for a share of the water such projects would save.