Sociopath and psychopath's psychology are naturally afraid of dying more than any good man who is willing to kill for survival, his family, etc. I say let them know you are very capable of doing so and they will most likely leave you alone. In other words grab your sword if you don't have one and learn to use it.
And then sharing half the water so we can both survive because being kind is important too.
It's only when the good man, because of his ignorance and lack of experience, gets into believing he needs to be disarmed and disadvantaged do those types of people tend to take advantage, because they then see the opportunity to act out their unfortunate psychology. My opinion.