You could die of thirst surrounded by water

If you can not see it then to you it is not there. If you can see it then it doesn't matter if anyone else can see it. Trying to convince someone what you see by telling them won't make them see it. You will have to open up their mind first by showing them from a different "point of view." Once they see it then it will be possible to open their mind to view it differently. It's like the old saying "You can lead a horse to water but you can't make him drink it". Now on the other hand if he sees other horses drinking it then he will want to drink it and after that whether other horses are there or not when you lead him to the water he will drink it because from his "point of view" it quenches his thirst.