the current synthetic grasses “perc”. The water DOES drain into the ground underneath – hence recharging the aquafer. It is not the same as an impermiable concrete which forces the water into the storm water system. Rain will soak into the ground similar to if it were real grass. If it’s a hard clay surface underneath the synthetic grass then it won’t drain… but it wouldn’t drain if it were real grass over hard clay.
Lawns in San Diego make no sense… they make sense in places with lots of rain like Pennsylvania, Western Washington, etc… but here you cannot maintain a lawn without irrigation. It’s a hold back to the old english estates where you had rolling hills and sheep to keep them cropped.
