|Background: Thermal waters have been showing different beneficial effects on the skin due to their physicochemical composition. The beneficial effect of thermal water in the treatment of some skin diseases may thus justify its use as an active ingredient in cosmetic formulations. The main objective of this work was to demonstrate the potential of incorporating thermal water as an active ingredient in cosmetic formulations. (2) Methods: A descriptive literature review was carried out by the analysis of scientific articles in PubMed and Google Scholar databases. Twelve thermal spring waters were found (Avène, Blue Lagoon, Comano, Cró, Dead Sea, La Roche-Posay, Monfortinho, Saint-Gervais, Salies-de-Béarn, São Pedro do Sul, Uriage and Vichy) with potential as an active in cosmetic products, demonstrated through in vitro studies evaluating the different activities/properties and clinical trials in healthy volunteers or with skin pathologies. (3) Results: For these studies, in natura thermal water as well as incorporated in cosmetic formulations were used. In in vitro studies, most thermal waters have been shown to have activities on membrane fluidity, skin barrier repair, antiradical, antioxidant, anti-inflammatory and immunomodulatory properties, proliferative activity, regulation of processes involved in ageing and moisturizing properties. In clinical trials, cosmetic thermal waters reduced skin discomfort through their soothing and exhibited moisturizing and anti-irritant properties. (4) Conclusions: The effect of thermal waters on the skin and the absence of side effects reported in different studies allows them to be used as an adjuvant or in the treatment of various skin disorders and may play an important role in the cosmetics industry. However, further clinical trials are needed to assess their effectiveness and safety.