bacteria can proliferate in poorly maintained water systems, posing risks to users. All species are potentially pathogenic, but () is usually the primary focus of testing. However, () also colonizes water distribution systems, is frequently found with , and could be a good indicator for increased risk of nosocomial infection. Anonymized data from three commercial testing laboratories afforded an analysis of 565,750 water samples. The data covered July 2019 to August 2021, including the COVID-19 pandemic. The results confirmed that commonly colonizes water distribution systems, being the most frequently identified non- species. The proportions of and generally remained similar, but increases in during COVID-19 lockdown suggest static water supplies might favor its growth. Disinfection of hospital water systems was effective, but re-colonization did occur, appearing to favor ; however, colony numbers also increased as a proportion of the total. While remains the main species of concern as a risk to human health, 's role should not be underestimated, either as a potential infection risk or as an indicator of the need to intervene to control 's colonization of water supplies.