In March people were claiming the state had 12 months of water remaining. Lets assume that number is holding and we've got about 7 months of water left.
If the entire state simply halted all urban and industrial water use, that would buy about 3 extra weeks before the state runs out of water. And that is in a scenario where 40 million people (and all non-ag industry) simply cease to consume water at all.
Not washing cars or watering lawns is a great emotional gesture, but nothing short of real policy or weather changes will make any meaningful difference.
This has happened before and in the past the state made a big deal about it and everyone panicked. But before we ran out of water, the biggest deluge of water hit California in decades and the populous prayed for sun instead.
I understand that personal use is nothing compared to agricultural use, but it's as if everyone will continue business as usual until all the water is gone, and then it feels like "shrug oh well guess we'll move".