noun
used bathwater; leftover bathwater
Refers to bathwater remaining in the tub after someone has bathed. Often used in contexts like reusing water for laundry or describing water that has cooled.
残り湯で洗濯すると節水になる。
Doing laundry with leftover bathwater saves water.
朝になると残り湯はすっかり冷めていた。
By morning, the leftover bathwater had gone completely cold.