Temperature-dependent microbial dynamics in touchless sensor faucets during short-term stagnation
Anran Ren (Chinese Academy of Sciences, Xuzhou University of Technology, University of Chinese Academy of Sciences)
Zihan Dai (Georgia Institute of Technology)
Xiaoming Li (University of Chinese Academy of Sciences, Chinese Academy of Sciences)
Walter van der Meer (Oasen, University of Twente)
Joan B. Rose (Michigan State University)
Gang Liu (TU Delft - Civil Engineering & Geosciences, Chinese Academy of Sciences, University of Chinese Academy of Sciences)
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Abstract
Microbial contamination in building plumbing systems poses significant risks to public health at the point of use. Stagnation and warm temperatures are well-known drivers of microbial regrowth, but the effects of common short-term stagnation in touchless sensor faucets—widely used for hygiene and comfort—remain poorly understood. Here we show that microbial water quality in touchless sensor faucets changes during short-term stagnation (0.25–10 h) at varying temperatures (10, 30, and 40 °C). We identify two pivotal time points—2 and 4 h—where microbial diversity decreases and Legionella pneumophila concentrations increase significantly, driven by accelerated chlorine decay and biofilm contributions. Heating to 30 °C maximizes microbial biomass (measured as ATP) but minimizes L. pneumophila proliferation, whereas 40 °C reduces biomass while promoting L. pneumophila growth. These findings reveal a temperature-dependent microbial water quality guarantee period of 2–4 h, beyond which flushing is necessary to mitigate health risks. Optimizing faucet temperatures between 30 and 40 °C could balance microbial safety, user comfort, and energy efficiency, offering practical guidance for managing water quality in modern plumbing systems.
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