Efficacy of copper-silver ionisation in controlling Legionella in complex water distribution systems and a cooling tower: Over 5 years of practical experience

Control of Legionella bacteria in water distribution systems and cooling towers is an increasing priority for health authorities world wide. Treatment of Legionella contaminated water is essential, and a well-recognized method to control Legionella is copper-silver ionisation. In this study the efficacy of copper-silver ionisation in 4 complex drinking water distribution systems (1 juvenile institution, 2 hotels and 1 penitentiary) and 1 cooling tower was studied over a period of at least 5 years. Dosing of 400 ± 200 μg/l copper and 40 ± 20 μg/l silver proved to be effective to control, abate and eradicate Legionella bacteria at all 5 treated locations. Legionella reoccurred only incidentally and temporarily (in 3.8% of the measurements; 27 out of 718), most likely due to insufficient flushing of the water distribution systems; in the case of the cooling tower technical malfunction of the tower itself and non-optimal positioning of the copper-silver ionisation system in the cooling tower. There was no evidence that pH (7.8-8.6) and hardness (1.4-2.3 mmol/l) of treated drinking and cooling water influenced the efficacy of copper-silver ionisation.