**5. Conclusions**

Water quality measurements, including hot water return line *Legionella* positivity, total bacterial counts, temperature, and other physicochemical parameters, have previously been sought or suggested as alternative approaches to determine the *Legionella* risk for a building's water system instead of directly culturing the system. We found a concordance rate of only 77.8% between hot water return *Legionella* positivity and distal site *Legionella* positivity. Additionally, using hot water return line positivity as a predictor for *Legionella* distal site positivity had a sensitivity of only 55% and a specificity of 96%. There was no significant correlation between *Legionella* positivity and any water quality parameter (HPC, temperature, incoming cold-water chlorine, or physicochemical concentrations) tested. Neither hot water return line *Legionella* positivity nor other water quality parameters are suitable as a surrogate or stand-alone replacement for sampling and culturing distal sites for *Legionella* colonization in building water systems, especially in facilities with higher-risk populations.

**Author Contributions:** Conceptualization, F.P.S.III and J.E.S.; formal analysis, J.L.B., X.M., and M.M.W.; investigation, D.P. and X.M.; writing—original draft preparation, D.P., J.L.B. and X.M.; writing—review and editing, D.P., J.L.B., X.M., F.P.S.III, M.M.W., and J.E.S.; visualization, D.P. and J.L.B.; supervision, F.P.S.III and J.E.S.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.
