We conduct in situ electrical conductivity measurements on water in a diamond anvil cell (DAC) under high pressure up to 28 GPa and study the electrical transport properties of water and ices.

In liquid state, the increasing rate of electrical conductivity with pressure is slower than that obtained in shock-waves measurements.

In solid phase, the relationship between electrical conductivity and pressure is discontinuous, which is corresponding to phase transformation from ice VIII to ice VII.

The difference in electrical conductivity of VI, VII, and VIII may associate with different orientational ordering in these ices.

The electrical conduction in these ices is dominated by already existing ions and Bjerrum defects, which play an important role in electrical transport properties of ices.