Occurrence of Legionella in Nonpotable Reclaimed Water

Legionella was monitored in reclaimed water systems and were detected by culture in 50% of 115 samples, while 80% of the samples were positive by quantitative polymerase chain reaction (qPCR). The lowest level of Legionella was in a system that practiced biological nutrient removal and maintained an average 0.3 mg/L free chlorine residual. The difference between qPCR and ethidium monoazide treated samples was used as an indicator of viability, and the greatest difference was in a chloraminated system, where the molecular method indicated a 9% viability. Ninety‐six percent of the species were L. pneumophila, and 87% were identified as L. pneumophila serotype 1. Total amoebae (summed as cysts or trophozoites) were detected in 100% of samples from all six systems, and were mostly (50–95%) in the active trophozoite phase. In the chloraminated system, 87% of the mesophilic amoebae and 66% of the thermophilic amoebae were in the cyst phase.