The original querent stated in a comment on March 3rd that they think it is "The Far Look" by Theodore L. Thomas.
The plot concerns a base on the Moon in the near future. Astronauts who spend time in the base return to Earth with vastly increased intelligence, but scientists are unable to discover what is causing this. The only outward sign of the change is a "far look" in their eyes, as if they see beyond any horizon.
The story follows two astronauts through their mission, with flashbacks to problems encountered in previous missions. The account is highly accurate from a science and engineering point of view. It also deals with psychological issues, such as the refusal of a previous pair to drink their recycled water because of its alleged taste. The replacement crew find them dead of thirst, and the water totally pure and tasteless. The dead men could not bring themselves to drink reprocessed human waste.
Only at the end does the reader find the truth: it is the return to Earth that alters the minds of the astronauts. Coming back to the cradle of humankind cleanses their minds of the baggage of their pasts and leaves "men of untrammeled mind".
The full text can be found in the archive.org copy of Astounding Science Fiction, August 1956.