noun
heated bathwater; hot water for bathing
Often refers to cold mineral spring water that has been heated to a suitable bathing temperature, as opposed to naturally hot spring water.
この旅館の沸かし湯は、冷鉱泉を温めたものだ。
The heated bathwater at this inn is made by warming cold mineral spring water.
沸かし湯と天然の温泉では、肌触りが違う。
Heated bathwater feels different on the skin compared to natural hot spring water.
Compound of 沸かし (wakashi, the continuative form of 沸かす 'to boil/heat') and 湯 (yu, 'hot water').