That's a funny way of saying "we didn't want to dry up the rivers", isn't it?
Isn't it really just a "feel good" thing?
No one is arguing about wet years either. Look at the dry year example. 36% environmental. 62% agriculture. 13% urban.
Edit: also notice the chart - the delta is only about half of those environmental percentages (on average, unfortunately they don't split it out for dry years). The other half comes from "North Coast" which seems likely to be more difficult to take advantage of - at least I haven't heard any controversy over trying to use that water. We don't know what the exact percentage would be in a dry year, but it would still be below 36%.
California needs to tackle water usage. There are reasonable changes that can be made in homes and towns - swapping to drought-resistant gardens instead of lawns, rain barrels to catch run-off, absorbent parking lots that don't drain out to the sewers, etc.
Agriculture also needs to be tackled, sure. That doesn't mean saving a percent here and there is of no use.
What really matters is the amount of water that can be channeled to your place of living today.
And then having small changes like non-flushed toilets help increase awareness about water shortage. If that ultimately makes people replace their lawn with desert plants, I think it's a win.