The people that complain that it’s way more complex than that are the ones that don’t want to pay for water.
The water we’re talking about doesn’t come through a pipe with a meter, and the people who have access to water have practical influence over the use, routing, safety, and quality of that water even if you try to assert legal control over them.
If that connects to a shared aquifer which can easily be depleted, then not without regulation.
> Draw surface water from a river, stream, or creek that passes through it?
I wouldn't expect to be allowed to reduce the flow of one of those, comparing how much enters and how much exits my land.
> Grow crops in their own flood plains, estuaries, marshes, ponds, and lakes?
That seems fine, probably.
Much of the water being discussed is in rivers and streams, which is taken as it passes through the land that uses it. It is only useful if it is in that exact waterway. There is no such thing as a market rate for water in a dry river.
If you turn it into an open market there are all sorts of weird complications. E.g. ranch A is upstream of Ranch B. Under a market system ranch A can use all of the water in the stream and just pay for it. Ranch B now doesn’t get that option since there is no more water in the stream. Rancher B can buy more water, but what good is buying water in a river that doesn’t go through your land.
So then you get to a rights based system. Rancher B has been watering his fields for 100 years, and rancher A comes along and says he wants to water his fields too. That’s fine, he just has to lay claim to whatever rancher B isn’t using.
The rights system would work fine except that nature won’t cooperate. We divided up rights for 100 units of water fair and square, so what do we do when we discover that we can only get 90 units of water.
Do you all take a 10% cut? Does the newest guy take the full cut (how it works now)?
You say it’s not complex, but millions of lives and industries worth trillions all rely on it. The current solution is a known flawed treaty that is almost 100 years old based on legal concepts that are far older. If it was so simple it would have been solved back then.
Why not go a step further and just "solve" water shortages around the world by "forcing" some neighboring country that has too much water to sell it to you at the same price as to themselves? They weren't using it anyway, so that's fair, right?
If you or I were Emperor, it would be easy. But the current US system is different.
