system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is California in a water crisis?

I heard that starting next month they're going to begin state wide water sanctioning which is pretty insane. How have we not fixed this yet? I've heard tons of people say it would be super easy to fix if they would just build purification plants and pipelines etc, which obviously cost money but I think water is something that we can afford to spend money on.
gpt
Most folks here aren't addressing the underlying reason *how* California got to this point of "crisis". 

The evidence suggests that California is recently exited a particularly wet period that lasted roughly 300 years. And during that period of time California has seen a huge influx of people who were attracted to the possibility of developing agriculture in the area (think forty-niners turned farmers). But now that the rain has stopped you are left with the population that settled the land with the expectation that it would be sustainable but with no more rain to sustain it.

The fact is California is a high-desert and there is a significant probability it will never go back to seeing the amount of rainfall that it did in recent years.  There is also a chance that what's going on is caused by cyclical climate changes and if that's the case California may see the rain return in several 100 or perhaps a 1000 years.