Recent investigations in the west coast region of Sweden has revealed the occurrence of groundwaters with a pH of around 4 and, further, alarmingly high concentrations of soluble aluminium. The reason for the occurrence of acid groundwater is, of course, the acid precipitation falling over this area of Sweden in combination with coarse soils on resistant types of granites and gneisses. The »resistance« against acidification of groundwater offered in the soil profile by aluminium and iron hydroxides must obviously have been partly broken. It seems therefore relevant to examine the solubility conditions of aluminium compounds in soils and rocks. From this we may reconstruct the process which led to the present state and we may also be able to tell what information on soils is needed in order to predict the future acidification of groundwater.