The great differentiating element of the Spa is the characteristics of its waters. A natural mineral water, commonly known as thermal water, has therapeutic properties with favorable effects on health due to the particularities of its physicochemical composition. This type of water is bacteriologically pure, circulates at great depth and its chemical composition is stable. Bacteriological purity is guaranteed through analytical control in the different collections, all circulation is carried out in stainless steel piping with smooth welds in order to avoid the accumulation of impurities and all the water consumed by the water collectors follows a rigorous analysis program coordinated by General Directorate of Health.

The rich chemical composition of thermal water is due to its circulation underground at great depth and at a very slow speed, normally on the order of a few meters per year. The water reacts with the environment and absorbs elements from the rocks, resulting in an evolution in its physical-chemical composition. These are the elements that give therapeutic properties to natural mineral waters and are the basis of thermal activity. The potentialities of the waters of Caldelas, already used by the Romans, were analyzed by Charles Lepierre in 1921, who considered them a “unique and unmistakable type among all medicinal waters”.