That’s because the Supreme Court said that’s not a taking except in extreme cases. See Lingle v. Chevron U.S.A. Inc., 544 U.S. 528 (2005) for the current state of the law on regulatory takings.

Which should open the door for regulating agricultural water use in California right? If California mandated that crops requiring more than X water per acre couldn’t be grown would that be a taking?

I don’t know if you could pass a law exactly like that, but it’s a good point that California could attack the problem from the other direction—-keep water law as is but squeeze the companies farming the desert using other parts of its regulatory toolkit.

Aye I’d also imagine that it is within the current legal framework to “tax” water property/rights in accordance with the allotment. It would be easy enough to exclude residential zoned water allotments from the taxes to avoid taxing drinking water.