Actually, it's more convoluted than that:

    Water that naturally flows into the state’s “wild and scenic” rivers, which are not connected to the state’s water system and can’t be under state and federal protections
    Water required for maintaining fish and wildlife habitat within streams
    Water that supports wetlands within wildlife preserves
    Water needed to maintain water quality for agricultural and urban use

https://www.sandiegouniontribune.com/news/drought/sdut-sacra...

I'm unable to tell whether that's a tally for untapped water or if it's really meant to account for something meaningful.

The CFB does say that ag accounts for 80% of "human use".