The present study was conducted in Sivas, Karabuk and Bartin regions of Turkey, which have rocks of different origins, agricultural and mining activities. Correlation, principal components, hierarchical cluster and multidimensional scaling analyses were applied to determine the processes controlling the chemical composition of groundwater. The results show that dissolution-weathering process, agricultural activities, oxidation processes of sulfide minerals, mining activities, coal levels, alteration of volcanics and progressive silicate hydrolysis effects the physicochemical properties of groundwater in the study areas. Principal components and multidimensional scaling analyses provided excellent visual representations of the grouping of the waters. The significant variables in the first factor are SO4, Mn, Fe, Al, and pH. The factor represents the groundwater reached by these elements via the dissolution and oxidation processes of sulfide minerals (especially pyrite). Ca, EC, and HCO3 are generally grouped under the second factor representing the dissolution of carbonate rocks. The third factor represented by Na, CO3, and pH is mostly related to alteration of volcanics, progressive silicate hydrolysis and dissolution, and probably ion exchange between Ca and Na. The fourth factor of NO3 and Cl is strongly influenced by agricultural activity. The measurement, analyses and evaluation results showed that the groundwater contamination is caused by (1) NO3 in waters discharging from clastic rocks in areas where intensive agricultural activities are conducted; (2) Al, Fe, Mn, and SO4 ions in water emerging from volcanics containing Pb-Zn-Cu ore deposits; and (3) Al, Fe, and Mn in water issuing from coal levels and altered volcanics. Some of these waters are used by adjacent towns for drinking, domestic, and irrigation purposes.