To your other problem, I fully understand the practical implications. Knocking the guy out and stealing his water is pretty unethical. However, coming to equitable terms is fairly easy. More humans can think one step ahead and just gouging the guy for all his posetions means he won't help you in the future. Long term, that is bad for you, thus you'll likely not charge too outrageous
For instance, why is making noises infringing on your freedom from noise, but the requirement of silence is not an infringement on your freedom to make noises? Freedom from noise and freedom to make noises are both "freedoms" and one comes at the expense of the other. What is the way to weigh their relative importance which is universally applicable to other cases and not rooted in culture or personal preference?
Another problem is whether it's OK to require a thirsty person in a desert to give up all their assets in exchange for water, and whether it's OK for the thirsty person to knock you out and take the water in response; most people would side with the thirsty guy for what I think are very good reasons in terms of the practical implications while objectivists would not.