I'm not an advocate of the St. George pipeline (actually against it), but from what I read, the upper basin states are currently using only 70% or so of their legally allocated water, and CA is using far more than their legally allocated Colorado River water. So upper basin states should be able to utilize more water, and CA should reduce their use to be within current law.
The problem as I hear it is that CA has no plans to reduce water use, and has implied that they will lock the entire Colorado River water use subject up in court for many years while still using more than their legal amount of water if push comes to shove.
One thing seems for sure though, the river system is over-allocated, and those allocations need to be altered - but I've heard of no movement to pursue this change from the powers that be. This seems to me like it should be a HUGE focus of our state and federal government, but it isn't.