Environmental Health Perspectives is an Open Access journal published by the National Institute of Environmental Health Sciences. Environmental Health Perspectives is an Open Access journal published by the National Institute of Environmental Health Sciences.

“Spa waters should be left untreated” says the dogmatic approach. Health authorities of European countries having traditional spa culture strictly control hygienic conditions of bathing in thermal/mineral waters. These regulations are based on the assumption that chemical treatment (disinfection) of such waters impacts their healing effects. However, a slow change of paradigm has been observed in studying the mode of action of spa waters that could help overcome recent attitudes. Organic content or the role of microbiome has also been emphasized by some authors recently. The article deals with possible interactions among aquatic microorganisms and the disinfection and health effects of spa waters and tries to explain the new findings in this field.