ABSTRACTConsiderable changes in water quality have been observed in ground water pumped from wells in quaternary formations in Poland. These changes include increases in dissolved calcium, sulfate, iron and manganese.Experimental results indicate that dissolved‐solids' increases are influenced by the introduction of oxygen into the hydrogeochemical environment during pumping.The oxidation of sulfur compounds produces acid, which increases the solubility of numerous chemical compounds. Bacterial catalysis of some reactions is indicate