The presence and prevalence of Legionella spp in collected rainwater and its aerosolisation during common gardening activities.

AIMS: To determine the presence and prevalence of Legionella spp in domestic rainwater storage butts and to quantify its aerosolisation when collected rainwater is used for common gardening activities.

METHODS: Volunteers were asked to take a water sample from their garden rainwater storage butt. The presence of Legionella was determined using quantitative polymerase chain reaction (qPCR). Two new rainwater storage butts were installed on-site at PHE Porton and positioned in sunlight or in the shade. Ambient conditions and those within the two 'experimental' water butts were continually monitored. A cyclone air sampler was used to detect the presence of Legionella in the air when collected rainwater was poured from a watering can or delivered via a hosepipe attached to a submersible water butt pump.

RESULTS: A total of 63 volunteers provided water samples from 113 different rainwater storage butts. Legionella spp was detected in 107 of these samples at a mean concentration of 4.7 × 104 genomic units l-1 . Two of these samples also contained L. pneumophila. The water butt positioned in the shade stored water at a significantly lower temperature than that exposed to sunlight. While the concentration of Legionella was significantly higher in this cooler water, meteorological conditions rather than conditions within the water butt had the greatest effect upon Legionella concentration. No Legionella was detected in the air when rainwater was poured from a watering can. However, using a hose pipe on a 'fine spray' setting increased both the number of organisms detected in the air and their dissemination.

CONCLUSION: In this study, Legionella spp were common contaminants of collected rainwater. However, the use of rainwater for common gardening activities should not be discouraged. Aerosolisation of Legionella when using a watering can is minimal and any increased risk associated with hose pipe use can be mitigated by using a coarse spray setting.