Water within a water tank is irradiated with ultraviolet light from a UV lamp for virucidal and germicidal purposes while simultaneously transforming oxygen molecules to ozone molecules in an oxygen containing gas flowing within an annular space defined by a sleeve surrounding the UV lamp. The ozone enriched gas flows into an enlarged chamber into which the UV lamp extends and the flow rate is reduced to enhance the time of exposure of the ozone enriched gas to UV radiation and thereby enhance the production of ozone. To increase the rate of transformation of oxygen molecules to ozone molecules, the gas is under a predetermined pressure prior to entering the annular space and subsequent to discharge from the chamber.