Abstract: This invention is a method and system for treating wastewater and for purifying and disinfecting drinking water. The treatment includes the addition of pressurized ozonated air to the pumped raw water stream by use of a venturi injector and then achieving well-mixed ozonated water by an in-line static mixer. This promotes the ozone reaction with pollutants in the raw water. The stream is then injected into the ultraviolet (UV) reaction chamber by a static impinger in the form of a conical spray nozzle. This breaks up the stream into a fine mist of one-micron diameter droplets falling down through the chamber. Air released from the droplets is suitably vented to keep the chamber pressure near atmospheric. At a lower plane in the chamber, a UV light source in the form of a uniform grid of essentially coplanar UV lamps irradiates the falling droplets to kill bacteria and viruses and also to catalyze the still ongoing ozone reaction.