Deionisation and clarification process of the aqueous medium used in an electroerosion machine and product for this process, where the electroerosion machines are comprised of a purification circuit for this aqueous medium, which includes an ion exchange phase between some cationic and anionic resins with the aqueous dielectric medium, which has a conductivity of less than 40 .mu.S/cm, and to which a solution of oxalic acid and phosphoric acid in distilled/deionised water is added in the approximate proportion of oxalic acid between 0.18 and 0.035 moles and phosphoric acid between 1.28 and 2.5 moles per liter of solution.