The grass bandaids on commercial lots is not captured by that 10% residential use figure. So all those dumb strips of grass on medians and in front of strip malls get counted in that 80% figure. A lot of that water is wasted by running off into drains.

Grass lawns are a waste of water, gas (mowing/maintenance), time, and effort. Reducing grass lawns in residential and commercial spaces would make for a meaningful reduction in the state's water usage with little reduction in economic output.

No, the 80% figure only includes agriculture. Not grass fields on commercial lots. Consider this: produce is mostly water. Now consider the weight of all the produce in California (including waste like corn stalks or potato plants) to the weight of all the grass lawns. 8:1 would be an extremely generous ratio in favor of the lawns.