During his reign Philip I/II of Spain had clearly set forth what the water rights laws were for each zone and region in the Spanish empire.
There are latin names for these zones BTW, but I don't happen to know them right off hand. But this stuff is in The Law Of The Indies if you wondered.
His son, Philip II/III, is the guy who decided to DIVIDE North America up among various European powers for purposes of development. Oregon was retained by Spain until the boundary with Russian North America could be determined ~ would it be 54/40, or further Souf ~ or maybe even at San Fran Bay eh!
Good thing for the Oregonians here that they eventually found an inlet along the Inland Passage to the North at about what is now the Southern boundary of Alaska. That pretty much cancelled the Russian claim to San Fran ~ and you know, of course, the history of Fort Ross, right?
What that also did was extend the customary water rights found in Arid and Semi-Arid lands to all of Oregon! Also to British Columbia, Wyoming, Montana, Idaho, Washington, and Northern California!
So, let's just say, Spain Did It ~ and it's been that way a very long time. Eventually the US purchased the territory, respected a handful of landgrants, and began selling it off ~ with Western Water Rights law in place ~ and there you have it.
Guy hasn't got a leg to stand on.
Thanks for the brief history lesson!!that was excellent!