In this paper the variation in radioactivity of eight spring waters of Estância de Águas da Prata, State of São Paulo, is presented. The methodology for the measure of radioactivity using liquid scintillation detectors is described in detail. The results were treated utilizing the "ACP" (Analyse en Composantes Principales) program. The following conclusions were reached: the variation in the radioactivity is related to the dry and wet seasons, this variation being caused by the dilution of spring water by rain water, thus decreasing the radioactivity values. This dilution is observed immediately in waters circulating in shallow aquifers (sandstones) during the wet season (summer). The dilution occurs later on, during the dry season (autumn-winter) in the spring water of deeper aquifers (volcanic rocks). The spring waters are considered as mineral waters with respect to temporary radioactivity and they can be classified as strongly radioactive (Villela and Vitória springs), radioactive (do Boi spring) and feebly radioactive (Prata-Radioativa, Prata-Nova and Platina springs).
