Constructed wetlands (CWs) have been developed in recent decades to treat several types of sewage effectively such as raw and secondary sewage. CWs are known to be a more sustainable alternative compared to the conventional systems. However, there are problems reported about CW when it could not remove pollutants by its design removal capacity. Thus, the performance and efficiency of CWs need to be studied in detail, especially when trying to understand the sustainability of the CWs. In this paper, a method of using a full-scale physical modeling was used for tracer study to evaluate the hydraulic performance in the systems. Physical modeling is normally preferred because it is easy to control the parameters as compared to the field test. Besides, a full-scale physical modeling is better when compared to a small-scale test in terms of justification of complex interactions of water characteristics inside the wetlands. In this paper, salt, as a tracer mass was injected into the CWs and the response was measured by examining the salt concentration exiting at the outlet. The outcomes of the results were acceptable when compared to the theoretical equation. With a better method of studying the efficiency of a CW, it is hoped that the concept could be adopted to understand the sustainability characteristics of a CW as well. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.