Legionella species: A potential problem associated with rain water harvesting systems?

Taylor, Judith A.; McLoughlin, Rory; Sandford, John; Bevan, Ruth and Aldred, David (2021). Legionella species: A potential problem associated with rain water harvesting systems? Indoor and Built Environment, 30(6) pp. 801–815.

DOI: https://doi.org/10.1177/1420326x20911128

Abstract

The risk of Legionella transmission from rain water harvesting (RWH)-fed water toilet flushing was investigated. Experiments monitored RWH tanks to determine Legionella spp. presence which was successfully isolated from three of four of RWH tanks (site 1: 3600 CFU/dm³ in February and 3600 CFU/dm³ in May; site 2: not detected; site 3: <940 GU/dm³; site 4: 44,000 GU/dm³), and to determine whether toilets could generate aerosol droplets capable of harbouring bacteria. The concentrations of particles measuring 10 µm or less in diameter (PM₁₀, capable of reaching the alveolar region of the lungs and causing disease) were monitored following flushes. Aerosols were detectable in an enclosed toilet cubicle (PM₁₀ concentration increased in one experiment from 0.038 mg/m³ when t = 1–600 s to 0.057 mg/m³ when t = 600–800 s). Recovery of Lactobacillus plantarum (surrogate for Legionella) from a seeded toilet cistern (108 CFU ml/dm³) indicated that bacteria were expelled, as demonstrated by recovery on MRS plates placed around the toilet unit. Legionella could be dispersed via aerosols from a toilet flushed with water from an RWH system and the effect would be more pronounced in smaller, enclosed areas, but this is unlikely to pose a risk to human health.

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