As far as I know California is already short on water. Would a sprinkler in every house system be sustainable or even possible in such conditions that everything burns?
You would have to have a pressurized water storage tank at each house. It would be quite expensive and have a lot of maintenance for how rare the usage would actually be.
CA has frequent water shortages, and is in drought conditions right now. Where would the water for the sprinklers come from? What is going to raise it from the underground water source to the roof level? Electricity, which may not be available? Are you going to retrofit a large and heavy cistern on every roof, that relies on gravity to distribute the water?
It can be done on a community level, not individual houses. In Portland, we have several HUGE water towers that hold tens of millions of gallons that supply pressurized water to neighborhoods, like the Denver Water Tower. They also have them on the ground in hills where you can't see them, supplying houses below. For fire suppression, it doesn't have to be potable water. It's just a quick thought I had. I know if I lived there and there was a fire breakout and heading towards me, I'd stick a sprinkler up there whether there was a water shortage or not.