Your math checks out - of the top of my head, 435,000 gallons is approx 1.6 million liters - 1600 m^3 * $0.4/m^3 = ~$640/acre of water, for $1440 of product, or ~ $800 profit (for just water costs)

One variable we are missing is transport costs - that $0.40 is for generation, and transportation of water from the ocean to the central valley would probably be expensive.

Alfalfa is also a nitrogen fixer, so on top of being something farmers can sell it reduces furtilizer costs.

Obviously your equation is a big simplification, but you’re missing a lot of the input costs.