‘污水’ literally combines ‘污’ (wū), meaning ‘dirty’, ‘filthy’, or ‘polluted’, and ‘水’ (shuǐ), meaning ‘water’. Together, they form a compound noun meaning ‘sewage’ or ‘wastewater’ — water that has been contaminated by human use, industrial processes, or natural decay. It is commonly used in environmental, public health, and infrastructure contexts, such as wastewater treatment, pollution control, and urban planning.

The term carries a neutral-to-negative connotation and is rarely used in casual daily conversation unless discussing sanitation, ecology, or city management. It is not interchangeable with general terms for ‘dirty water’ like 脏水 (zāng shuǐ), which refers more broadly to visibly unclean water (e.g., muddy rainwater or used dishwater) but lacks the technical and systemic implications of 污水. In formal writing and official reports, 污水 consistently denotes water requiring treatment before reuse or safe discharge.