Mechanistic modeling of Legionella in building water systems: A critical review on the essential factors

Modeling Legionella exposure from building water systems is valuable to inform water management plans, but accurate risk estimates require accounting for spatiotemporal variations in concentrations. This comprehensive literature review covers existing mathematical approaches for predicting Legionella fate and transport in building water systems and proposes a framework for advanced modeling considering all mechanisms influencing its presence in water and biofilm during different life-stages (e.g., within protozoan hosts). Current models include persistence of culturable cells in a heater, growth and decay throughout simplified hot water systems, concentrations linked to water age using fitted growth rates, and a calibrated model for a highly-monitored system. The challenges of modeling influencing factors are also discussed, including water demand, hydraulics, nutrient availability, pipe materials, temperature, and chemical disinfection. By contrasting laboratory and field observations with existing models, this review highlights knowledge gaps and data needs for integrating Legionella growth and persistence into hydraulics, water quality and, ultimately, exposure models to define minimal-risk design and operational practices.