御湯[oyu] hot water
塩湯[shioyu] hot salt water (incl. bath)
温湯[ontou] comfortably hot bath
下湯[shimoyu] sitz bath
そと湯[sotoyu] open air bath (in an inn, onsen, etc.)

給湯[kyuutou] hot-water supply
給湯器[kyuutouki] hot-water heater
腰湯[koshiyu] sitting bath
重湯[omoyu] thin rice gruel
出で湯[ideyu] hot spring