Quality of an Underground Hydro Resource in Order to Classify it as Natural Mineral Water for Thermalism: The Case of the New Resource "Termas de São Tiago"

A Medical Spa in Portugal to work legally needs to be supplied by a groundwater that is classified as natural mineral water. After the referred classification, that water is considered as a geological resource and of the public domain, that is, protected by the Portuguese State. Among several studies, mainly hydrogeological, the quality of that natural resource and its physicochemical and microbiological stability, over a hydrological year, is absolutely crucial to obtain the official classification of the resource. Thus, the main objective of this paper is to present the fundamental elements of that domain, in the sense of presenting a case study, which serves as an example to other situations. The results of physicochemical and microbiological analysis, performed monthly, for 12 consecutive months, as well as, the results of a very complete analysis with trace chemical elements, gases, radiological parameters, mineral oils and polycyclic aromatic hydrocarbons, are presented, analysed and discussed. Finally, the main hydrogeochemical classifications of that natural resource are presented, which led to the new mineral water called as "Termas de São Tiago", and which was responsible for the fact that Portugal can currently count on a new medical spa in operation.