A new method is disclosed for the electroerosion machining of a workpiece by employing as a machining fluid, raw water which has been deionized until its resistivity increases to at least 105 ohm-cm and then decreasing the resistivity of the raw water deionized previously by adding thereto a conductivity modifier substantially free from chloride ions, said conductivity modifier being added to said deionized water in an amount sufficient to impart to the resulting machining fluid a predetermined conductivity.
