Relevance. Despite many years of research on water from the Chulymskaya well, there are still contradictory and incomplete data on dissolved organic matter and the isotopic composition of water, in addition, new geochemical data have accumulated that were not previously presented. Aim. Based on the material accumulated over 20 years and new data obtained, further study the geochemistry of natural mineral water Omega with an emphasis on the isotopic and organic composition, including the first presentation of data on polycyclic aromatic hydrocarbons. Objects. Groundwater from the Chulymskaya well; data on other groundwater in the region are also provided for comparison. Methods. Standard analytical methods for studying water chemical, organic and isotopic composition. Study of changes in water composition over 20–30 years and comparison with other groundwater in the region under similar geological conditions. Results and conclusions. The data on the chemical composition of mineral water have been collected for 30 years and new data have been obtained, which shown its stability over time, however, sampling in summer is not recommended. Information on all available indicators of dissolved organic matter is presented, which does not allow classifying Omega as water with increased dissolved organic matter. Moreover, dissolved organic matter concentrations are lower than for other groundwater in the region. The polycyclic aromatic hydrocarbon composition in this water was presented. This showed the prevalence of high-molecular polycyclic aromatic hydrocarbons over low-molecular ones, in particular, dibenz(ah)anthracene prevails (39%). Isotope studies shown a fairly typical composition of the water itself (δD, δ¹⁸O) and a very variable composition of dissolved carbon δ¹³C_DIC from –30.3 to –10.7‰. The authors insist on its biogenic source, changing under the effect of various biogeochemical processes, the study of which is to be understood in the future.