The concomitant effects of hydraulics and reaction kinetics on the disinfection efficiency (DE) of Chlorine Contact Tank (CCT) setups were experimentally assessed, to test the predictive-ability of first order kinetics models: Chick-Watson (C-W), C-t rule and Wehner-Wilhelm (W-W). Prototype tests were conducted using river water characterised for quality parameters, chlorine demand and inactivation rates of total and thermotolerant coliform. Poor, average and superior CCT baffling conditions were assessed by tracer experimentation and for their DE under three chlorine dosages. The models' DE predictive-ability was comparable and high for superior baffling, but decreased differently with the hydraulic efficiency (maximum errors of +15.3% with W-W, +26.0% with C-W and -36.6% with C-t). The positive bias shown by W-W renders it unsafe for CCT design, so the results favoured the C-t rule as the preferred analytical tool of comparable complexity. Potential refinements to these models that could lead to operational savings are identified.