The mineral spring in Sofia Gorna Banya district has been known since the Thracians. The first study and description of this water was made as early as 1887. Subsequent analyses show that it has a constant physico-chemical composition and is microbiologically clean. This is due to its depth (more than 600 meters deep, which excludes any external pollution and adverse weather conditions) and the absence of ingredients that change over time. Experimental studies with mineral water Gorna Banya have shown that after its artificial contamination with some bacteria, for a period of 10 days it suppresses their development and has a purifying effect.