noun
bathwater
Refers to the water in a bathtub, typically in a Japanese-style bath (風呂).
風呂水が冷めてしまった。
The bathwater has gone cold.
風呂水を抜いて掃除する。
I drain the bathwater and clean the tub.
風呂 means 'bath' or 'bathtub', while 風呂水 is the water inside it.
Compound of 風呂 (bath) and 水 (water). The reading ふろみず is a straightforward combination of the two elements.