Guides
Three pieces, and they are ordered the way the problem usually unfolds: noticing that something is wrong, establishing how wet the building actually is, and finding out where the water came from once there is something growing.
The three
Why these three and not the usual ones
Each of them exists because of something specific about this region rather than about water damage generally. The water bill matters here because there is no rainy season to prompt anyone to look, which leaves the utility's meter as the only thing keeping a continuous record. Moisture readings matter because the coastal air makes "dry to the touch" actively misleading — a wall in Manhattan Beach in June feels finished long before it is. And the inspection piece leads with finding the source rather than identifying what grew, because on this coast the growth turns up months after the water, far enough back that nobody connects the two.
If it is happening now
These are for reading rather than for an emergency. If there is water on a floor at this moment, the useful page is emergency water removal, which covers the order things need to happen in.