Inactivation of Escherichia coli in water was experimentally studied, with pulsed electrical discharges in a hybrid gas-liquid reactor. The pH was dramatically decreased from 7 to similar to 3 within 60 min, accompanying with a 6-log reduction. To evaluate the contribution of pH on inactivation, a set of experiments were designed and tested. Results indicate that the contribution of low pH to the inactivation could be neglected compared to that of electrical discharges. On the other hand, the decrease of pH could be eased as carbonate or phosphate buffer was added to the treated water. However, the inactivation efficiency was greatly reduced because the buffers could deplete the active species formed in electrical discharges. Besides, a new finding is addressed in this paper that the water after plasma treatment still owns a certain extent of inactivation ability, functioning like the free chlorine residual. The environmental adaptation ability of E. coli to electrical discharges was also investigated. (C) 2009 Elsevier B.V. All rights reserved.