When combined, `水土 (shuǐtǔ)` becomes a metaphor for the natural environment and local conditions of a place. `不服 (bùfú)` means to not accept or not get used to something. Therefore, the idiom literally means “not accustomed to the local water and soil,” a powerful and vivid way to describe the feeling of being physically or culturally out of sync with a new environment.
`水土不服` is an extremely common term used in everyday life.