Modeling contaminant degradation is fundamental to the design, operation, and regulation of reactive contaminants in water treatment reactors. The plug flow reactor (PFR) t10 model has represented residence time distribution (RTD) in pathogen regulation for more than 25 years despite known limitations. Alternative RTD models have been developed, including the tanks‐in‐series (TIS), segregated flow (SF), and reactor network (RN) models. Tracer data were gathered from 35 reactors and their RTDs modeled using the PFR, PFR t10, TIS, SF, and RN models. Predicted contaminant degradation across reactor models was studied, and guidance was developed for selecting RTD models at different log reduction values (LRVs). This study demonstrated that the PFR t10 model may overpredict contaminant degradation at LRVs >2‐log and that the TIS, SF, or RN model should be used for these higher LRVs. A graphical method was also developed for rapidly screening predicted treatment efficacy for a range of contaminants.