On the eastern side of the US water rights are under a “riparian” system based on common law that tries to make water more or less equally available to anyone in the area

On the western side, in theory all the water was free for anyone to use originally but once you put a certain amount to productive use, you have a right in perpetuity to draw that amount from that source.

So all river flows, well-tapped groundwater, etc. were eventually all spoken for, and owning a piece of land doesn’t inherently give you a right to even the water on that land, you’ve got to obtain water rights separately if you want to use water for anything. And so it’s water barons as much or more than land barons that are, ah, upstream of the economy.

This is why LA building its aqueducts wasn’t just a story of engineering triumphs but political skullduggery, and so much Big Politics has been about water.

This is what Central Valley farms growing incredibly thirsty crops like almonds and alfalfa (to become beef) in a regularly drought-stricken desert is about – they have senior water rights, so they know they’re entitled to a certain volume every year.

That’s why it can be illegal to capture rainwater on your property - that’s water destined for rivers or aquifers where it already belongs to somebody else.