This is a dumb issue 
They are farmers in the Central Valley.  The water they “control” is in the Kern Water Bank, and is a massive underground aquifer that is under farmland they own or control.
They are seed and nut farmers - almonds, pistachios, pomegranates, etc.  all require a large quantity of water - more than most other crops.  
So having water rights is a necessity of their business, and owning the water beneath their land is no different than owning gold in the soil. 

The rest is just stupid conspiracy theories.