The present invention relates to a system and method for decontamination, sterilization and purification of water. A scalable reactor and method for treatment of contaminated water is disclosed. The reactor simultaneously combines ozone infusion, ultraviolet (UV) irradiation and ultrasound (US) vibration in one reaction zone. The process dramatically increases reaction efficiencies and allows greater volume flow of contaminated water for treatment. The process has been found to reduce contaminants in different types of water and applications, including potable, drinking, recycled for pools or aquariums, oil field, waste or recycled industrial water.