This study assessed the performance of a new most probable number test (Pseudalert (R)/Quanti-Tray (R)) for the enumeration of Pseudomonas aeruginosa from swimming pool and spa pool waters by comparing it to the international and national membrane filtration-based culture methods for P. aeruginosa: ISO 16266:2006 and UK The Microbiology of Drinking Water-Part 8 (MoDW Part 8) which both use Pseudomonas CN agar. The comparison was based on the calculation of mean relative differences between the two methods conducted according to ISO 17994:2014. Using both routine pool water samples (149 from 8 laboratories) and artificially contaminated samples (309 from 7 laboratories), paired counts from each sample and enumeration method were analysed. For routine samples, there were insufficient data for a conclusive assessment, but the data do indicate at least equivalent performance of Pseudalert (R)/Quanti-Tray (R) to the reference methods. For the artificially contaminated samples, the data also did not result in a statistically conclusive assessment but did indicate potentially better performance of Pseudalert (R)/Quanti-Tray (R). Combining the data from the routine samples and artificially contaminated samples resulted in an ISO 17994 outcome that the two methods were not statistically significantly different. Thus, the Pseudalert (R)/Quanti-Tray (R) method is an acceptable alternative to ISO 16266 and MoDW Part 8. The Pseudalert (R)/Quanti-Tray (R) method has the advantage in that it does not require confirmation testing, and of providing confirmed counts within 24-28 h incubation compared to 40-48 h or longer for the ISO 16266 and MoDW Part 8 methods.