An association of firms that make and sell so-called 24-hour-baths said Feb. 10 it will introduce voluntary sanitation guidelines for the water used in the systems.

The guidelines, to be introduced in April, call for limiting the number of the Legionella pneumophila bacteria to less than 10,000 per 100 milliliters. The association decided to take the step in an apparent attempt to appease user concerns over the pneumonia-causing bacteria. An earlier survey conducted by the association found that the number of bacteria exceeded 10,000 in 14 percent of 350 examples inspected.

The 24-hour-bath system, which saw a boom in recent years, is installed with a unit that purifies and circulates bath water, always keeping the water warm. Concerns have been raised, however, that bacteria could be unleashed in the self-purifying system.

Association representative Masatoshi Sakai emphasized that there have been no reports of people becoming sick from the 24-hour-bath system. However, he said, the association decided to adopt the guidelines to save the market.