Abstract: A method and apparatus are disclosed for treating water, either potable water or a recirculated body of water, in which the water flows through a passage around and in direct contact with the surface of the germicidal ultraviolet lamp and in direct contact with at least one ozone producing ultraviolet lamp, whereby dissolved oxygen in the water is directly converted into ozone dispersed in said flowing water. The water, when part of a recirculated flow as in treatment of pool or spa water, also flows in contact with a predominantly copper element having an extended surface, whereby ions of the copper are taken up in the water. The copper element preferably is a pair of spaced apart copper electrodes across which is applied an electrical potential by a control which maintains a constant current and thus regulates release of copper ions into the water for inhibiting growth of algae. The UV lamps are subjected to ultrasonic energy which will loosen particles tending to cling deposit on the lamp surface.