Formal — to staff
Onsen · Sento
You
あの、すみません。この小さいタオルは湯船の中に入れても大丈夫ですか？
あの、すみません。このちいさいたおるはゆぶねのなかにいれてもだいじょうぶですか？
Um, excuse me. Is it okay to put this small towel into the bath water?
Romaji: Ano, sumimasen. Kono chiisai taoru wa yubune no naka ni irete mo daijōbu desu ka? / Reply Romaji: Iie, yubune ni wa irenaide kudasai. Atama ni noseru ka, karada o fuku no ni tsukatte kudasai ne.
Reply
いいえ、湯船には入れないでください。頭に乗せるか、体を拭くのに使ってくださいね。
いいえ、ゆぶねにはいれないでください。あたまにのせるか、からだをふくのにかってくださいね。
No, please don't put it in the bath water. Please put it on your head or use it to wipe your body.
Gesture & etiquette
Hold up the small towel while asking. Staff might make a gentle 'no' hand gesture or point to the head.
Never put the small towel (face towel) into the main bath water. Only the large bath towel is used for drying after bathing, not inside the bathing area.