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. Enlist your accommodation's help to call ahead.
Even paid in full, the cost of medical care in Japan is low compared to countries like the US. 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.
The only insurance accepted at Japanese clinics and hospitals is Japan-issued health insurance; however, they cannot refuse treatment for lack of insurance. For any medical treatment you'll have to pay up front (credit cards are accepted at hospitals and may or may not be accepted at local clinics) and apply for reimbursement when you get home.
No vaccines are required for travel to Japan.
24-hour care is available at major hospitals.
Every city neighbourhood or town has at least one primary care clinic. Called naika (内科), these are often small – sometimes run by just one doctor – and are considered the first point of contact for common, non-urgent complaints, like rashes, sinus infections, gastric upsets and the like. For additional care, the doctor can refer you to a specialist.
There is no requirement in the Japanese system to register with a particular primary care doctor or clinic. Most naika accept walk-ins; in fact, many do not take appointments. Be prepared to wait and note that most close for several hours during the early afternoon.