Japan?s celebrated onsen, or hot springs, are embroiled in a national scandal amid revelations that several inn owners have been surreptitiously filling their baths with tap water, outraging thousands of Japanese and damaging the industry.

The purity of onsen water, which contains minerals believed to have a therapeutic effect on various ailments, is an issue the Japanese treat with utmost gravity. Overworked salarymen and their families often spend more than Y20,000 ($180) a head for a weekend escape to an onsen resort, in which they can melt away the stresses of cramped, urban life in Tokyo.