Japan enjoys a high level of medical services, though unfortunately most hospitals and clinics do not have doctors and nurses who speak English. Even for those that do, getting through reception can still be challenging.
University hospitals should be your first choice; doctors are most likely to speak English and the level of care is usually highest. Larger cities, especially Tokyo, are likely to have clinics that specialise in caring for the foreign community; these will have doctors who speak English but they will be pricey. Most hospitals and clinics will accept walk-in patients in the mornings (usually 8.30am to 11am); be prepared to wait.
Expect to pay about ¥3000 for a simple visit to an outpatient clinic and from around ¥20,000 and upwards for emergency care.
Tap water is fine to drink in Japan; in some rural areas, locals swear by its health benefits.
No vaccines are required for travel to Japan.
The only insurance accepted at Japanese hospitals is Japanese insurance. For any medical treatment you'll have to pay up front and apply for a reimbursement when you get home.