Assessing the health risks associated with the usage of water-atomization shower systems in buildings.

In the context of climate change policies, buildings must implement solutions to reduce energy and water consumption. One such solution is showering with water atomization showerheads, which can significantly reduce water and energy usage. However, the lack of risk assessment for users' health has hindered the widespread adoption of this technology. To address this gap, we assess the risk of spreading bacteria, in particular the pathogenic bacterium Legionella pneumophila, from shower hose biofilms of different ages grown under controlled or uncontrolled conditions considering different levels of water hardness, during showering using water atomization showerheads (ECO) or continuous flow showerheads (STA). We compared the aerosol and bioaerosol emission - total, viable and cultivable - during a 10 min shower event between the two shower systems. We showed that the water-atomization showerhead emitted slightly more nanoparticles smaller than 0.45 µm and slightly fewer particles larger than 0.5 µm than the continuous flow showerhead. Additionally, ECO showerheads emitted fewer cultivable bacteria than STA, regardless of the biofilm's age or growth conditions. When Legionella pneumophila was detected in biofilms, ECO showerheads released slightly less cultivable Legionella in the first flush of shower water compared to the STA, ranging from 6.0 × 10 to 1.6 × 10 CFU·L. However, cultivable L. pneumophila was not detected in the aerosols emitted during showering with either showerhead. These findings suggest that emerging water-drop emission technologies might affect human exposure to aerosols differently than traditional systems, emphasizing the importance of assessing the health risks associated with any new shower system. Additionally, these findings provide valuable insights for achieving a balance between water and energy conservation.