Public Health Risks Associated with Aerosolised Pathogens from Non-potable Applications of Recycled Water

Water scarcity threatens global health and development, prompting increased adoption of recycled water. However, recycled water introduces potential health risks due to pathogenic microorganisms. Aerosol-generating applications of recycled water are particularly concerning yet understudied. This systematic literature review examined the human health risks associated with aerosols generated from non-potable applications of recycled water. Ten peer-reviewed articles from the United States, France, China, and Israel assessed infection risk using quantitative microbial risk assessment (QMRA). These studies focused on aerosolised exposure to four pathogens: Legionella pneumophila, Escherichia coli, Staphylococcus aureus, and norovirus genogroup I and II through inhalation and dermal contact. Infection risks for L. pneumophila and E. coli from toilet flushing ranged from 2.95 × 10⁻⁶ to 8.52 × 10⁻⁵ and 8.8 × 10^–15 to 8.3 × 10^–11 infections per person-year (ippy), respectively, all within the United States Environmental Protection Agency (USEPA) limit of 10⁻⁴ ippy. For irrigation, risks for L. pneumophila ranged from 1 × 10^–12 to 1.3 × 10⁻² ippy and for norovirus from 1 × 10⁻³ to 8.1 × 10⁻³ ippy. Other applications included fountains (≥ 7.96 × 10⁻⁴), cooling towers (1 × 10⁻⁴ − 1 × 10⁻²), dust control (1.71 × 10⁻⁵ − 8.78 × 10⁻⁴), and S. aureus through dermal contact (2.7 × 10⁻⁷). Most studies estimated aerosol dose indirectly using source water pathogen concentrations and exposure scenarios, contributing to variability in predicted risks. These findings highlight the need for microbial risk assessment models incorporating direct exposure measurements to estimate pathogen concentrations in aerosols across applications.