The precursory anomalies of hydrochemical constituents at No. 107 well of Tanggu waterworks in Tianjin are rather apparent in the Tangshan earthquake. But since July 1986, the ionic concentrations.in large magnitude have been detected in the well. In order to study the variational cause of the ionic components, the pumping test and the field investigaion were performed. The results obtained are helpful to explain water quality anomalies, to eliminate the interference factors for other pumping well and to understand the anomalous mechanism.