The electrical conductivity of water, compressed by explosively driven shock waves, has been measured in the experimentally difficult range of relatively low pressures (20–100 kbars). The results link the earlier high-pressure data of David and Hamann and of Yuknavech with the results of static experiments at much lower pressures. They confirm that the high conductivity of shocked water arises from enhancement of the normal self-ionization of water. In addition, experiments have been carried out to determine the effects of changing the initial temperature of the water, and to compare the behaviour of shocked D2O with that of H2O.