The optimization of polymer dose during the coagulation and flocculation stages of drinking water treatment remains a challenge for treatment plants. Incorrect polymer dosage can lead to negative effects downstream, environmental effects, negative health effects and increased polymer costs. Analytical methods are not suitable for on-site monitoring, and it is particularly challenging to accurately detect and measure very low polymer concentrations in drinking water. This study employed an in-line and real-time UV-vis spectrophotometer to measure the polymer concentration in raw and treated water by correlating polymer concentration to the absorbance at 190nm and introduced a new approach to improve the sensitivity and detection limit of the method through altering the path length. In addition, the method was used to determine the optimum polymer dose required for treatment to prevent the addition of excess polymer during coagulation/flocculation. The method has the potential for development into a full-scale optimization system.