10% of water in California is used for urban needs, it’s more likely agriculture will get hit by water shortages first than population growth. But then again, the permitting process is already limited to an extent by available water resources, it’s part of the infrastructure needed to build.

Re-routing water from far-away farms to metropolises will take time, so it's DEFINITELY possible that we'll see water shortages in major cities.

Agriculture often has the more senior water rights, so I wouldn’t be too sure.

Either way they can’t wring any more water from urban users. Rural users will get hit 90% faster than urban users as water becomes more scarce simply because they consume more now.

No- if water becomes more scarce, those with junior water rights don’t get water. The end. Those with senior rights get just as much as always. So the question is not whether you are ag or rural or muni, it’s how senior are the rights you hold?

The state will simply invest more to bore water down from Northern California. But that won't be enough to satisfy agricultural needs, and farmers will have no access to the water that is brought down. Heck, for urban users, even desalinization is economical, but not for agricultural users.

And how long since we consider that an ever growing population is not a good thing for the environment?

When I read medias like Bloomberg, they seem legitime in their climate change coverage, but they always lament the slow growth of US's population.

That's likely coming from different reporters talking about things from different angles. A shrinking population is a potentially big economic issue it puts stress on all sorts of things chiefly the Social Security system in the US (and those like it in other countries).

Ultimately I don't think we'll be able to population shrink our way out of climate change, at least not on timescales and in ways that people are willing to accept. It's just coming too fast and the population changes so slight that it's not going to come in as a last minute solution.