California is allowed to use any available water source to fight fires. That could include your pool. I'm not sure if you are allowed to put something over or near your pool to discourage them from taking a few thousand liters a scoop as you want it for your roof sprinkler. A roof sprinkler is 20-50 gpm. My pool is relatively small and it's 13000 gallons (but if you pump it empty, it may pop up like a boat). Even at 100 gpm and leaving some water in the pool, that is days of sprinkler use. You normally need far less than that.
A decent redundant system would cost tens of thousands (two ICE pumps in parallel contained within a structure that allows air flow but minimizes chance of fire). Starting it at the right time and getting away is not simple. I know some municipalities that encourage roof sprinklers have you set everything up and leave the open frame honda pump sitting on your front lawn and fire fighters start all the pumps as the fire approaches. It takes some effort from them but it also helps them do their job.
