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drainage; ditch; gutter; sewerage
sewage; black water
「下水」 has another reading with different meanings.
下水管が詰まって修理を依頼しました。
The sewer pipe was clogged so I requested repairs.
大雨で下水が溢れて道路が冠水した。
The sewage overflowed in the heavy rain and the roads flooded.
下水の臭いが気になる。
The smell from the sewer is bothersome.