Traditional public bathhouses in Japan are in deep water as soaring energy costs triggered by the Middle East oil supply disruptions threaten to extinguish the fires of a fading tradition, with some of them forced to shorten their hours or even shut their doors for good.

Already struggling with a shrinking customer base and ageing owners without successors, the oil price surge is dealing a fresh blow to sento, as the communal baths are known in Japanese, with regulated pricing making it...