What are the required breakdown electric field magnitudes (Volts per meter) to form a DC arc in water and air?

Question

I saw once that it takes 3 MV/m to ionize air to make it conductive. Is this true? What is this value for distilled water under normal/average conditions? Is there such a value for water?

Answer 1

Yes, that is true. The average sample of air will break down and become conductive at 3 million volts for meter. This is known as the dielectric strength of the material.

Pure water has a dielectric strength of about 81 V/m. Water with dissolved ions will conduct electricity freely, so it has no dielectric strength.