[ac29]

Agricultural water varies in price greatly but it is often like 1000x cheaper than residential water in CA.

Its not the treatment process - I think a substantial portion of actual costs of water is in delivery. This source estimates 2GW needed to move water around in California on peak days: https://energy.lbl.gov/publications/water-supply-related-ele... That's about 5-10% of total electric use in the entire state.