1. E. Pentcheva, L. Van't, E. Dack, V. Veldeman and R. Hristov. Gijbels, Hydrogeochemical characteristics of geothermal systems in South Bulgaria. University of Antwerp (UIA), Antwerp, 1997.
2. Deutsches Institut für Normung Standards DIN 38406 Part 3 Cations (1982); DIN 38405 Part 19 Anions (1988); DIN 38405 Part 20 Anions (1989).
3. Bulgarian Governmental Standard BDS 14947 Natural Potable Mineral Waters (1980).
4. L. Vladeva and D. Kostadinov, Bulgarian mineral potable waters, Part 1, M-8-M, Sofia (1996).