How about the Columbia? Average discharge is 265,000 cfs, which has been pretty consistent over the past 100+ years.[1] That's approximately 200 million acre feet just flowing into the Pacific every year.

For comparison, the Phoenix metro area uses 2.3 million acre feet of water per year (40% of which is used in agriculture).[2] So a bit over 1% of the Columbia's annual flow.

Another comparison: the Colorado "in its natural state" averaged just 22,500 cfs, less than 10% of the Columbia.[3]

I'm not saying that piping water from Oregon to the southwest is a good idea, but it's not as if we don't have water in the west. It's just a lot further north than most of the population centers.

[1] https://en.wikipedia.org/wiki/Columbia_River#Discharge [2] https://askabiologist.asu.edu/questions/how-much-water-are-w... [3] https://en.wikipedia.org/wiki/Colorado_River#Discharge