noun
fresh bathwater to pour over oneself
Refers to clean hot water used for rinsing the body before entering a communal bath, or for a final rinse after bathing. Common in onsen and sento contexts.
温泉では、まず掛かり湯をしてから湯船に入ります。
At a hot spring, you first pour fresh bathwater over yourself before getting into the bath.
かけ湯 is a more common synonym with the same meaning; 掛かり湯 is a less frequent variant.
Compound of 掛かり (kakari, 'pouring over') + 湯 (yu, 'hot water'). The exact historical derivation is uncertain, but the term is conventionally associated with bathing practices.