From where?

I don't understand how that's possible. I don't know of any lakes or rivers or aquifers larger enough to provide water to almost 40 million people in California.

The Sierra Nevada watershed

https://www.nature.org/media/california/california_drinking-...

The large greenery to the right is the Colorado River which provides 15% of CA water at the bottom.

Sierra Nevada watershed is already being used by Northern California.

It provides 60% of California water.

Even removing the farms, I couldn't find any data supporting that it was enough water for the rest of California.

But that doesn't necessarily mean that it can't either.

The data I found says the Sierra Nevada watershed supports 750,000 farms.

Is that equivalent to 15 million people or so?

Californian agriculture is 80% of water usage. That agriculture is largely shipped out of state, internationally, and supplying the rest of the US half of its produce outside staple grains: fruits, nuts, vegetables, berries, etc.

> If you reduce the ag water usage that is shipping most of that produce to the rest of the country,

Those aren’t gifts to the rest of the country (and, actually, much of it is exported directly internationally), they are cash crops, and the lifeblood of rural California.

This whole thread I responded to was about CA self-sufficiency and I was specifically arguing that CA can be quite self-sufficient.

> California would immediately become a failed state on its own, unable to meet even the most basic needs of its residents

Of course CA independence would be economically harmful and disruptive. Doesn't mean CA won't be able to provide its own water by taking an ag trade economic hit.