water heater; domestic boiler
Refers to a device that heats water for household use, such as bathing or kitchen taps. Often used in contexts like apartments, homes, and commercial facilities.
We installed a new water heater, so the bath heats up quickly now.
The water heater is acting up and there's no hot water.
electric water heater
Compound of 給湯 (kyūtō, 'hot water supply') + 器 (ki, 'device'). The term is straightforward and modern, with no obscure historical derivation.