Pacific gopher snakes from the desert? Hmmm...I grew up in the Bay Area, and I caught plenty of Pacific gophers, but that habitat was more grassland/oak-scrubland than actual desert...Here in Phoenix, we have actual desert, and there's no pacific gophers here.....I know they are a wide ranging subspecies, and they do occur in many different biotopes, but I'm not thinking that desert is one of them....
All that being said, yes. Supply your new snake with an ample supply of fresh clean water at all times. They are not a "desert subspecies" (in the same manner as a Sonoran sidewinder is) and as such, any change in humidity level from a water bowl won't make things "too humid".
-Kris