The word "水蒸气" is formed by combining three characters: 水 meaning "water", 蒸 meaning "to steam" or "evaporate", and 气 meaning "gas" or "vapor". These are assembled in a logical sequence where 水 specifies the substance, and 蒸气 together denote the state of that substance as gaseous steam, resulting in a compound that literally means "water steam gas" or water vapor.