Abstract
Eco-friendly showers aim to lower energy and water consumption by generating smaller water droplets than those produced by traditional systems. To evaluate the risk of users inhaling the contaminants associated with such water droplets—namely, chemical components or opportunistic bacterial pathogens such as Legionella—we modeled the behavior of water droplets aerosolized by water-atomization technology at a flow rate of 2.2 L/min and compared the results obtained using this model with those determined experimentally in a typical shower stall. Additionally, we monitored the number and mass of inhalable water droplets emitted by twelve showerheads—eight using water-atomization technology and four using continuous-flow technology—which have distinct characteristics in terms of water flow rate, water pressure, spray angle, and number of and diameter of nozzles. The water-atomizing showers tested not only had lower flow rates, but also larger spray angles, less nozzles, and larger nozzle diameters than those of the continuous-flow showerheads. We observed a difference in the behavior of inhalable water droplets between the two technologies, both unobstructed and with the presence of a mannequin. The evaporation of inhalable water droplets emitted by the water-atomization showers favored a homogenous distribution in the shower stall. In the presence of the mannequin, the number and mass of inhalable droplets increased for the continuous-flow showerheads and decreased for the water-atomization showerheads. The water-atomization showerheads emitted less inhalable water mass than the continuous-flow showerheads did per unit of time; however, they generally emitted a slightly higher number of inhalable droplets (1.6 times more), including those large enough to carry a bacterium each—only one model performed as well as the continuous-flow showerheads in this regard. Further experiments are needed to assess whether this slight increase in the number of inhalable water droplets increases the biological risk.
Highlights
While endotoxins commonly aerosolized in showers are rarely of sufficient concentration to impact human health [6], the inhalation of water aerosols containing opportunistic bacterial pathogens (OBPs)—including, among others, Legionella pneumophila, nontuberculous Mycobacteria, and Pseudomonas aeruginosa—during routine showering has been regularly implicated in life-threatening respiratory infections [7,8,9]
The computation predicted that a water-atomizing showerhead with a flow rate of 2.2 L/min generates 211.8 × 106 inhalable water droplets per second
This number increased with the distance traveled by droplets and doubled at the maximum distance considered of 2 m when the relative humidity (RH)
Summary
While the microorganisms responsible are naturally present in almost all aqueous media, they prefer to install and form biofilms in water pipe systems in which water stagnates, where the water temperature is between 20◦ and 45 ◦ C. Under such conditions, they can reach sufficiently high numbers that—when detached from biofilm, carried by the water flow, and aerosolized, e.g., during showering—they represent a risk of infection to the user
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