浴

Three drops of water on the left, the contracted form of 水. The indexing radical here. Bathing is a water activity, so the radical is literal. Same radical heads 河, 湖, 海, 洗, 漂, the family of water actions and water bodies.

Right component supplies the sound (gǔ → yù, a regular Old Chinese drift between velar and zero initials in the same rhyme). 谷 itself depicts water flowing out of a valley mouth, which adds a strong semantic echo: bathing was originally done in valley streams. So 浴 is etymologically 'water flowing through a valley = where one bathes'. Same phonetic in 欲 (desire), 俗 (common), 裕 (abundant).