The main aquifer formation consists of sedimentary series of the Quaternary period, drained mainly from the Kheto and Desaguadero Rivers. Measures for electric conductivity of underground and superficial waters, as well as the results of hundreds of physicochemical analyses, allowed the definition of different hydrogeochemical areas. Waters from the Titikaka Lake (Desaguadero River) are the sodium-chloride type and show high concentrations. In the high waters season, these rivers transport salinity to flood plains in the Oruro area, where salt is concentrated by evaporation. Likewise, groundwaters in flood areas present strong mineral contents in contrast to groundwaters in high spots of the hydrologic systems. Facies bicarbonated and carbonated waters are found currently at the bottom of the Paleozoic formations. Sulphated waters were observed in the Cenozoic series where gypsum deposits outcrop. -from English summary.