Alternative Disinfection in Hot Water Networks: Persistence and Antimicrobial Efficacy of Silver-Stabilized Hydrogen Peroxide for <i>Legionella pneumophila</i> Control

Engineered water systems operate under diverse chemical and physical conditions that influence disinfection efficiency. Hot water networks (HWNs) exemplify this issue, as thermal control is costly and ineffective in cooled sections, and chlorine degrades rapidly at elevated temperatures. Consequently, HWNs remain challenging for controlling pathogens such as Legionella pneumophila. Sustained HWN protection requires a thermally resilient, persistent disinfectant. This study evaluated the stability and efficacy of silver-stabilized hydrogen peroxide (SSHP) in ultrapure, synthetic, and chloraminated municipal tap waters incubated at elevated temperatures for up to 72 h. Culture-based enumeration showed that SSHP antimicrobial efficacy increased with temperature, achieving >2.4-log reductions of L. pneumophila within 5 min at 55 °C. SSHP retained full biocidal activity after 72 h at 60 °C in synthetic tap water, whereas free chlorine lost antimicrobial activity after 24 h. In municipal waters, total and free chlorine decayed below recommended thresholds within 24–40 h at 60 °C, whereas SSHP retained effective residuals after 72 h. Although these controlled experiments cannot capture real-system complexity, SSHP persisted under thermal conditions that accelerated chlorine decay, supporting its use as a resilient HWN disinfectant. This work demonstrates how system-specific evaluation of disinfectants can inform improved strategies for managing microbial risks in water systems.