Mutsumikan

Spring-source temperature

55°C at the source

Bathing temperature

42°C at the stated use point; this is not guaranteed as a fixed temperature for every bath or time

Spring source

Gero Onsen water; the inn does not identify a separate individual source

Spring classification

Alkaline simple spring

pH

9.18

Flow rate

Not published for the inn

Water handling

The inn calls its system semi-free-flowing. Fresh spring water is continually added, while some water is filtered and recirculated to remove sediment; overflow is drained rather than reused, and filtered water is not returned through the fresh-water inlet. The inn also says spring water is used in the large-bath showers and taps. This is not a fully non-circulating, 100% free-flowing system.

The inn is not currently open for general day-use bathing. Its outdoor bath closes from midnight to 05:00; the public bath normally closes by 09:00 the next morning and may close at 08:00 on cleaning days. Some room baths are explicitly described as onsen; a room listed only as having a bath is not assumed to use spring water. Tattoo rules are unconfirmed.