Why didn't California use desalination plants before the drought got this bad?

The reason they didn't look at using them before, is because Desalinization is a "stop-gap" measure, not a solution.

Pardon the phrase, but it's "#$%^#%^ where you live/eat." From the article, each gallon of fresh water produced, produces a gallon of brine which is dumped back into the ocean, which in turn threatens the marine life.

California is an Arid Plain. Though it can support a lot of people it really never should have supported as many people as live there now. It has hit "viral" levels of humanity, and areas like San Francisco/ Oakland & Los Angeles / San Diego are just too populated.

Add in the farm crops, industrial, etc, and we have the "boat with a hole" issue. You can only bail water so fast. Or in this case, we're using it far faster than we can recover.

Lack of foresight?

Solar desalinization would be even cheaper than fuel-fired plant, albeit slower.

I had always heard that desalination was way too expensive to be a reliable option. I never bought that excuse. Quite frankly, I would be willing to bet that if they did try and use desalination plants, the EPA would come in and stop them because they were endangering some form of wildlife like the spotted elfen whorehound, or some other such thing.

In the end, I believe this was foreseeable, and I think California only has itself to blame for not funding water replenishment projects. They could have spent their money in more deserving programs like this than throwing all that money into what they did to put them in their financial dire straits.