The United States and Mexico agreed Tuesday to new rules on sharing water from the Colorado River, capping a five-year effort on how to spread the pain of drought and reap the benefits of wet years... Mexico will forfeit some of its share of the river during shortages, bringing itself in line with western U.S. states that already have agreed how much they will surrender when waters recede. Mexico also will capture surpluses when waters rise...

The agreement, coming in the final days of the administration of Mexican President Felipe Calderón, is a major amendment to a 1944 treaty considered sacred by many south of the border. The treaty grants Mexico 1.5 million acre-feet of river water each year - enough to supply about 3 million homes - making it the lifeblood of Tijuana and other cities in northwest Mexico.

"We have chosen collaboration over conflict; we have chosen cooperation and consensus over discord," said U.S. Interior Secretary Ken Salazar, who called the new pact the most important international accord on the Colorado River since the 1944 treaty.

Mexico will begin to surrender some of its Colorado River allotment when the elevation in Lake Mead drops to 1,075 feet and begin to reap surpluses when it rises to 1,145 feet. Mexico will be allowed to store up to 250,000 acre-feet of water in the reservoir and draw on nearly all of those reserves whenever needed...

"These are big political steps for Mexico to take," said Jeffrey Kightlinger, general manager of the Metropolitan Water District of Southern California, which will buy some of Mexico's water. "Chances are we won't have a surplus and we won't have a shortage, but if we do, we'll have the guidelines in place on how we're going to handle it."

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