I know this is going to be a long shot but my father read a book around 1965-1967 about a space explorer who goes to a planet (he believes it is Mars) where he meets two warring alien tribes. One tribe is short and fat and one tribe is tall and skinny. He also remembers part of the story where the explorer believes one alien is urinating into the water supply and contaminating it but the alien is actually purifying it. Does this sound familiar to anyone? Thank you in advance.
ETA: He says this is not the novels with John Carter in them.