@Suspect D
To understand the problem with John and the water supply, we have to first understand the most common libertarian property rights theory, which is based on
John Locke's concept of homesteading.
In nature there exists some water. Then the first human arrives and he begins to use that body of water. This first use constitutes the highest claim, that is no one else can say they were there first.
That's important, because property rights help resolve conflicts. If I know that this piece of land is mine, then if you want to use it, we know you need my permission. If neither of us own it, we're going to fight over who gets to use it, with no one to determine the winner except violence.
But to establish ownership, we need clear title, either first use, or a chain or exchange of that property that legitimizes my claim to it.
So if John got the water first, that is he was the homesteader, and he is an asshole, then people who would rely on the water probably wouldn't have settled there.
Let's say John buys the water rights from the original owner, you, and then suddenly becomes an asshole to everyone drawing water from his property.
1. It is likely people would have already established contracts for water use, which John would be compelled to take on.
2. John would be investing in a valuable and presumably expensive resource to get no return.
3. The people in the surrounding area would likely be hostile and stop trading with John if he denied them access to water.
4. People would trade with John for water.
These are in my opinion, likely scenarios. Only #2 is particularly problematic. If #2 happens, people who did not contract for water usage, and do not have an alternative source, will have to move.
This is an unlikely scenario, because I am unaware of any water supply which is exclusively owned in North America for example. Most water sources have multiple rights holders, with
easements being used to determine the extent one rights holder can effect the resource.
But, for the sake of argument, let's say that a mean jerk with a lot of money manages to buy up an entire water supply. Yes, that would suck for the people already there. They would have to pay to bring water in, or sell their land and move. This would probably drive down the value of John's water rights, but if he is mean and crazy, then maybe he doesn't care. He certainly won't have the wealth (or the same wealth) to do that stunt again. He will also damage his reputation in a free society by being anti-social. People will be less likely to want to work with someone who behaves in such a negative manner.
Scenarios like this are similar to "What if Aliens attack?". It's basically a license to theorize a potential threat scenario and construct the parameters in a way which deliberately stresses the libertarian argument. It's usually a short cut around theory and knowledge, and a gotcha game of emotional appeals (similar to, "what about the poor?").
One has to understand in debate, the mindset of the people who propose this stuff. It's a position of fundamental fear and paranoia. Indeed, many of the people arguing in this thread for government are scared or indicate a high level of concern about what would happen if they had to be responsible for their own safety.
When someone is so paranoid of change and bad outcomes, it clouds their capacity to think rationally. To weigh costs and benefits. To take chances and try new things. There is a reason why so many successful people, from athletes, to musicians to business folk are libertarian and not socialist. It's a forward thinking, risk taking social philosophy based around respect rather than insecurity. Successful people tend to have a lot of confidence.
Government and the media do a great job of pitting people against each other, keeping everyone paranoid, everyone separated and divisive. This is the status quo. Hindu vs Muslim, Democrat vs Republican, Black vs White etc.
Ayn Rand had a good answer to a similar question, iirc on the Phil Donahue show. She said (paraphrasing) that nothing essential for life, was so scarce that one person could possibly own it. And when you think about it, that's true and makes the "What if Aliens attack!?" or "What if John is a mean rich guy?!" arguments seem really strained and weak.
When people are so obsessed with security as the people who argue for government are, you can't do much about it. Our most powerful instinct is fear. It's a defense mechanism sometimes, but more often than not, it is used to control us.
Also, the libertarian answer to the water supply is that we should utilize contracts to build lasting relationships for resource security. That's the way that property rights can be limited as a weapon against others.