The world produces far more calories of food than is needed, so water impact per calorie is a dumb metric since calories aren't the critical figure of merit.
What matters is water impact per $ of dependent economic activity.
You're missing the point that we are talking about regulating water usage external to the industry (in which people should and do care about water usage as it relates to sustainability of California as a whole), and water usage internal to the industry (in which an individual farmer cares about yields, efficiency, and economic value of crops).
Internal to farming the entire reason we have so many almonds in CA is exactly because it's a high-efficiency and high-value crop.
https://slate.com/business/2015/04/almonds-in-california-the...
"In a real sense, the almond industry is the future of California agriculture—high value, high efficiency, but still high consuming. That’s not necessarily a bad thing, as it makes most sense to use a scarce resource for the highest value application possible."
Well, no, because I was positing a better metric for competing agricultural uses, not the one-true-metric for all uses and, also, because even if it was the one true metric for all uses, unless water was the limiting factor for urban economic production, while it kight imply all cuts needed fron current consumption should cone from ag, it wouldn't imply additional cuts to ag to increase urban alotment. And, while the reverse allocation of cuts would cut all urban use in a foreseeable shortfall (because its such a small share to start with) any shortfall that would require ebough cuts to equal all agricultural use would be a a cataclysmic disaster no matte how the cuts were apportioned (and most would cone from agriculture because, even after you stopped giving any to people—whom you need for agriculture, anyway—you’d barely have dented the necessary total cuts.