A computational fluid dynamic (CFD) model of an ozone contacting chamber in the Umgeni Water Wiggins Waterworks in Durban, South Africa, has been set up and verified by experimental tracer tests, as part of an investigation to optimise the control and disinfection efficiency of the contactor. The effect of gas injection was modelled by increasing the turbulent intensity at the reactor inlet. Experimental tracer responses which were used as partial verification of the model correspond very closely to model predictions.