I don’t know what the Supreme Court thinks, but I’m not convinced. If the government takes away your land or your building or your gold, that’s eminent domain.

I don’t know what the Supreme Court thinks, but I’m not convinced. If the government takes away your land or your building or your gold, that’s eminent domain. But these water rights are permission to take water in the future that may or may not ever show up (and increasingly does not show up), and they may de facto not be usable regardless of any government action. Alternatively, don’t take them away — just tax them. Set a price for water such that there is no scarcity (keeping in mind that the money collected can be used to reclaim, desalinate or otherwise acquire more water), and let anyone else buy water at the same price, and poof they’re still there but no longer worth much.