Water treatment

A process for treating water comprising organic micropollutants and/or microorganisms comprising:

• treating the water using an energy source and adding to the water an additive, wherein the energy source is UV radiation and the additive comprises performic acid,
• wherein the water to be treated is subjected to UV radiation during continuous addition of the additive containing performic acid to the water and the performic acid is added to the waters to be disinfected and/or subjected to degradation in an amount of 0.1 to 5 mg/l and intermittent instantaneous shock dosing using performic acid in an amount of 10 to 50 mg/l is performed and a weekly sum of the shock dosage periods performed is 0.3-30 h.