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Table 1 Hypothesized effects of increased water use frequency under various hot water system operating conditions on L. pneumophila in distal taps

From: Water heater temperature set point and water use patterns influence Legionella pneumophila and associated microorganisms at the tap

Conditiona Dominant impact Hypothesized result Experiment herein
I. No disinfectant and low water heater set point (T < 48 °C) Growth due to increased delivery of nutrients to distal taps at ideal growth T Greatest total numbers produced in distal taps with time but lower concentrations due to more frequent use Control system, over time (T = 39 °C)
II. No disinfectant and moderate water heater set point (T = 48–51 °C) Low-use condition provides optimal ecological selection by transient sub-lethal T events Lower numbers produced in distal taps and lower concentrations at higher use Exp. 2 (T = 51 °C)
III. No disinfectant and high water heater set point (T > 55 °C) Re-growth limited only to distal taps during stagnation events Lower concentrations Exp. 3 (T = 58 °C)
IV. Stable and high disinfectant Disinfection effect dominates Lower number and concentrations Not tested in this work
  1. aSee Fig. 2 for hypothetical temperature effects from the literature