If the resources were not in use by anyone, then it is just for him to appropriate it. For example, if there was a flowing river that people drank from, it would not be just for him to claim this resource. If the river was polluted and he built a plant that purified the water, it would definitely be just for him to be the sole owner of that purified water. How could it not be? If he digs a well and draws water from it, who else is owner of that water?

Now if people rely on the water from his well as there is no other source of water there, then they still do not have the right to steal from him this water if they otherwise die. It is his water by right of appropriation and no one else's. He mixed his labor with nature and created value that he owns, and it is his to distribute.