Water is a polar liquid with a high electrical permitivity (εr = 80) and a specific electrical conductivity
σ. For a time τ of exposure of water to an electric field, when τ ε/σ, the aqueous
solution behaves as a dielectric medium, while for much longer times (τ ε/σ) it behaves
as a resistive medium. Deionized and degassed water (σ < 1 µS/cm, ε/σ > 7 µs) has been
commonly used as a dielectric in pulse forming lines for the generation of extremely high pulse power (P > 1 TW) with very short pulses (T < 100 ns) [1]. For a short line charging time
(t < 1 µs), the breakdown electric field E is ∼500 kV/cm and the corresponding energy density
W = εE2/2 ∼ 1 J/cm−3
. Breakdown in de-ionized water has been mostly studied to optimize
design of pulse forming lines.