Short story or novel from the 1970s or before about two warring alien tribes

Question

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.

Answer 1

The bit about mistakenly thinking an alien was urinating in the drinking water is pretty distinctive, and it matches Out of the Silent Planet by C. S. Lewis, the first novel of the Space Trilogy. There are multiple types of aliens on Mars: hrossa, pfifltriggi, and sorns; the sorns are extremely tall and look very threatening to the main character who has been kidnapped from Earth.

The only thing that does not match is that the aliens are not really at war, although I believe that the protagonist initially thinks that there are hostile aliens and friendly ones.