I read your question as one involving communities, as opposed to individuals, since that has been answered above.
My answer is that these issues are handled like most other issues - by a bunch of people sitting around gossipping and bickering and bullshitting and somehow finding a way to live with each other. I know that doesn't fit on a flow sheet very well, but that is how people have managed to live with each other for thousands of years, and we'll just have relearn these things.
Because if they can't find a way to live with each other, then there will be conflict and it can escalate to the point that people get hurt, and people get killed. And since the people getting hurt are your friends and your family, there is a great incentive to find some other way to work this out; and since the other communities are suffering the same, they feel the same need to de-escalate and work things out. Or your grandmother will kick your ass.
Armed conflicts tend to be perpetuated by Rulers throwing cannon-fodder they don't give a shit about at each other; when the dead have faces and names and meaning to you, and you have any real say in what happens, then wars don't happen. Conflicts, yes; fights, yes; feuds and vendettas and petty personal bloodletting, yes of course; war, not so much - because you, and I, are the cannon-fodder and we decline. (This assumes, of course, that everyone involved is acting in more-or-less good faith - which leaves out the usual suspects. And of course, those places and times in a resource death-spiral, where pretty much everyone is going to die anyway and they are fighting over who gets to die last.)
To specifics, water use can be very effectively managed by communities acting in cooperation, not through formal organizations and government agencies but just people talking to each other honestly. Irrigation canals in central and south america have been maintained by indigenous communities for centuries, without central organization, despite interference from conquistidors, missionaries, and national governments. Here it is important to understand that everyone downstream is entirely reliant on everyone upstream; this would be a situation that a capitalist would exploit to hold those downstream to ransom, yet this never happens - if you were to suggest such a thing everyone would stare at you as if you were a deranged idiot.
Right of trespass is common in most cultures (even in english common law, forced upon them by the peasants no doubt), as long as you don't harm the land or fuck with your neighbor's sheep everyone just waves and carries on. This runs up against Anglo/American "property" nonsense, i think.
Access to a localised, special resource is interesting. While one group could, in theory, seize and hold that resource to exploit all those others who would like use of that resource, in practice that only works when the group can use mass violence in the form of state armies or corporate mercenary militias. If a small group tries to sieze a resource, and pisses off _all_ of their neighbors in the process, then they are not going to survive long.
Traditionally, these resources were either shared as a commons (managed by customs to prevent catastrophic depletion), or occupied by a single group that gifted them to whoever asked for them.
You will run across examples of this again and again if your eyes are open to it. So yes, there is hope we can work with people who aren't Us, if we are all willing to try to work things out (and rearrange previous arrangements that aren't working).
If, on the other hand, you are dealing with a sociopath dumping mine waste in your Wild, or fracking your village - well, some people you just can't reason with ...
