I hear from people with no particular expertise in California water issues that we can't have people keeping on moving to our state, especially to the part of the state where those people live.
And I think that's right, iff we keep the same policies and same current water use patterns. That iff could well be right, changing policies is hard. OTOH, here are three facts:
About 20-25% of California water use is urban, where the vast majority of people live and where the overwhelming majority of population increases are occurring. A majority of that urban water use is for landscaping, either residential or commercial. We could virtually eliminate that use and supplement landscaping with graywater, allowing us to double the urban population with no increase in potable water demand. And if virtually eliminating lawns isn't politically feasible, see point 3.
About 75-80% of water use is agricultural, creating about 2% of California economy. At the simplest level then (okay, simplistic), reducing ag water use by 25% would also allow doubling California's urban population while costing 0.5% of the economic output. Hopefully the farming community will be aware of this and encourage innovative ways to conserve water in both urban and agricultural areas. The economic and political risk is obvious.
Recycled non-potable water, recycled water for drinking, shallow aquifers for non-potable use, and desal of brackish groundwater are all new urban water options that limit the pressure for #2 and the severity of #1. That's not even including ocean desal, which I think is mostly a bad idea, but if we are truly in the worst-case scenario of a 100-year drought then even that could play a role.
Summary: other developed countries like Australia and Israel have shown compatibility with far lower per-capita water use, and we've got additional technological options for water.
Behind this, I'll lay my own biases on the table: the US has chosen to support policies for a lot of population growth in this country, with a lot more people having American-sized ecological footprints. Not my choice, but given that, I think California is a good place to put a lot of those people, at least in the Bay Area and coastal SoCal where most of the people will go.* We have a smaller ecological footprint here, and our policies other than the egregiously-bad tax policies are pretty good, so why not here. And it's a nice place.
So that bias might color my conclusion, but the opposite bias is in place for many people who've said water is the reason why things shouldn't change from what they remember things to be.
*Also far north California, Redding and west to the coast where there's lots of water, but few people will end up there. It's in Sacramento and points south and east that you see more typically-destructive patterns of urban growth. Some growth will happen there, but that's not where most people will end up