Of course this is how some humans interact, but we still live in a pre-civil society. I'm not going to pretend I know into detail how a real free and civil society should look. And that is exactly the point: Neither do you. If you did, you should be made dictator of the world and I'd probably support you The best way to create a civil society in my opinion would be to let the market (i.e. all of us) find the solutions to complex problems. That's what free markets do best. The market can supply defense agencies, law enforcement, etc. just like it already supplies basic necessities today like food, shelter, clothing, insurance, etc.

So in short, your solution to have a "civil" society is to use violently enforced political structures? Your solution is to use force to have group B to give up the resource? In the end you'd have to be willing to kill to enforce that. I don't see how it is a valid argument to use force, coercion and violence to get what you want in any non-theoretical scenario.

But for the sake of argument I'll bite.

You say group B has plenty of water. What is the reason that these people don't want to give up their surplus of water? If they have plenty, wouldn't it be in their own economical interest to trade with group A instead of outlawing themselves from the rest of the world? Because surely the rest of the world would take notice and refuse to deal with these people. I think it would not be in their own interest to refuse to trade if they had such a rare and valuable commodity.

Secondly, can you think of any resource in real life, that is

1) as rare as you described
2) necessary for life
3) can be held hostage by one group of people
4) cannot be engineered around (drinkable water can be created in many other ways)