What is to stop California from using Mexico's surplus storage and refusing to give it up in times of drought when Mexico needs it? The upper basin has already "lost" a substantial part of their rights, since the lower basin borrowed the surplus while the upper basin was developing and is now playing the "shoot, but we really need this water" card, even though the upper basin needs it as well. The 2007 pact to push water from Lake Powell down to Lake Mead to equalize the two reservoirs is a perfect example of the lower basin's greed, eh hem, sorry, *need* overpowering the original spirit of the agreement. For decades after the 1944 agreement we never honored Mexico's allotment from the original division, and what water we did send, up until the 1970s, was so saline that it was basically unpotable. So we built a multi-million dollar desalination plant on the border, realize it's waaaaay too expensive so run, and instead opt to dump Arizona wastewater into the Mexican desert in order to just barely meet the water quality requirements under treaty when the water crosses the border (google Cienega de Santa Clara)...
Alls I'm saying is, there is not enough water or altruism is the basin to ever create a fair division - the whole thing needs to be redrawn.
“May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view. May your mountains rise into and above the clouds.”-Ed Abbey