Yes, drinking water from taps in Japan is safe. For environmental reasons, try to use a refillable water bottle rather than buying bottled water in Japan. Metro train stations have public water fountains, but otherwise these can be hard to find (this is the land of vending machines after all).

Yes, you can absolutely drink the tap water in Japan; it is consistently ranked as some of the cleanest and safest in the world. The water is strictly regulated by the Ministry of Health, Labour and Welfare, which monitors 51 distinct quality parameters to ensure it meets or exceeds World Health Organization standards. Throughout Japan, from Tokyo's high-rises to remote mountain villages, tap water is potable, and restaurants almost universally serve it for free. In larger cities, you might notice a very faint taste of chlorine, which is used to maintain safety in the extensive pipe network, but this is a matter of personal preference rather than a health risk. Many public parks, train stations, and shrines even feature dedicated drinking fountains. Most travelers find that carrying a reusable bottle and refilling it from the tap is the most eco-friendly and cost-effective way to stay hydrated while exploring. If the water is ever not drinkable (for example, in some very old buildings or specific industrial taps), it will be clearly marked with a sign.