The trees they're trying to keep alive have ridiculously high water consumption, almonds for instance consume 10s of litres of water for each _individual_ almond.
They need to stop growing trees like that in a desert, which is what they're doing.
The wells they are digging are tapping into the underlying aquifers that are the last resort, so they are in fact getting _free_ water while complaining about the cost. In essence they are stealing the water that other californians pay for.
At the same time they are asking for subsidies, to support a business model built on the ridiculously stupid idea of growing high water use crops in a _desert_.
The solution is to actually treat this as a free market (as most HN commenters seem to believe is the solution to everything), everyone pays the same amount for water, including farmers. This would mean farmers would actually make sane use of their water - maybe they can't grow almonds for a profit anymore, and switch to something else. They will probably fairly quickly find some new food stuff that people really want to pay lots of money for, but uses less water.
That's how things work.