お湯が

Hot water (as the subject of a sentence).

→ 御湯
phrase Rare #45,673
Hot water (as the subject of a sentence). お湯 means hot water, typically for drinking or cooking; が marks it as the subject.
JA: お湯が全然沸騰してない。
EN: The hot water isn’t boiling at all.

お湯が全然沸騰してない

The water isn't boiling at all.

— Tampopo (1985)

お湯が熱かったのね

So the water was hot, huh?

— 8 1/2 (1963)