The frequency dependence of impedance is studied in a capacitance cell filled with water directly contacting the electrodes. The absolute impedance value is determined by measurement of voltages in the cell and over the known resistance connected in series with it. The impedance dispersion range is found in the range of 104–106 Hz, where it decreases from the maximum to the minimum values. The processing of the impedance data using the corresponding equivalent circuit shows that distilled water has a constant dielectric permeability value (78–80 a.u.) in the whole studied range of 50 Hz to 10 MHz and impedance dispersion is related to dispersion of conductivity of water. An expression is obtained for description of conductivity of water at low, intermediate, and high frequencies (0–100 MHz) analogous to the Debye relationship. The value of τ = 0.6 μs and the value of the limiting high-frequency conductivity of 3 mS/m (at 20–25°C) is found for the additional conductivity dispersion region.