Quick answer: Water does not harm a stoma: pouches are waterproof, so you can shower or bathe with the appliance on. Many colostomates can also bathe briefly with it off. For onsen and sento, small bathing pouches, discreet skin-tone appliances and a pre-visit call to the facility make hot-spring trips entirely possible.
Bathing is one of the biggest worries after stoma surgery — and one of the easiest to solve. The pouch is waterproof; water won't enter the stoma. Shower with the pouch on, or, if your output pattern allows, briefly without it.
Onsen and sento
Japan's bathing culture deserves its own playbook: compact bathing pouches, skin-tone minis, a small towel carried naturally, and choosing quieter hours all help. Facilities differ, so calling ahead avoids surprises. Ostomate-friendly inns are increasingly common.