Per acre doesn't seem like the right metric.
(Discussed here: https://www.huffingtonpost.com/entry/lawn-largest-crop-ameri...) (original here: http://www.isprs.org/proceedings/XXXVI/8-W27/milesi.pdf)
If you look at aggregate water usage for California agriculture uses 4X "urban" and "urban" includes industrial, golf courses, parks, etc.
So even if lawns are using more area they are much less water intensive than agriculture.
Either way, the point that agriculture takes a lot more water than people watering their lawns still stands.