How many millions of illegal immigrants are using up water in the dry area of the Colorado River basin? That’s clearly part of the math.
All urban use by residential, industrial and commercial is only 25% of total basin water use. Residential is half of that so 12.5% figure 4:1 legals to illegals so 3 ish percent almost a rounding error even being generous with the 25% of every person in the Colorado basin that’s 10 million illegals alone.
Agriculture is the issue, specifically growing crops like alfalfa that demand FIVE FEET of water per square-foot of land area per year. Clearly that is not sustainable.
We have plenty of rain east of 100W to grow grass for cows with.