ABSTRACT: The objects of the study were springs in carbonate complexes in the Veľká Fatra mountains (Central Slovakia). These springs are tapped and used as the drinking water resources for the public water supply "Pohronský skupinový vodovod" (PSV). Program PHREEQC proved to be the right medium for modelIing carbonate balances. Chemical composition of groundwater in the catchments of Harmanecký brook and Starohorský brook is typical for fissure and karstfissure systems of limestone-dolomite complexes. Partial pressures of CO2, by which the water was mineralized, correspond to the values of partial pressures of CO2 in the soil atmosphere. Groundwater is in right balance with calcite and aragonite and slightly unsaturated in dolomite. It is obvious that without high amounts of CO2 the water is not getting saturated. Trend analysis for the time period between 1995-2000 show increase in saturated water in respect to carbonate minerals. One of the causes is the change in precipitation quality and change in catchments area in given locality.