As I understand it, the water situation is all kinds of screwed up, but much of the residential water is sustainable. SF, for example, uses mostly surface water and has access to a lot of surface water. One might argue whether the dam that supplies the water is a good thing or a bad thing and whether the allocation of SF’s water is reasonable, but it appears to be sustainable. In addition, residential water usage just isn’t that much.

Agricultural water in the drier parts of California is an entirely different story.