Water cooling towers (CT) are facilities designed to promote the exchange of heat between a fluid, usually water that has been heated by heat recovery in a process of installation, and air. There are different CT configurations, but their principle is similar: to cool a hot liquid by spraying into an air current. Hot water is usually sprayed at the top of the tower before descending by gravity against the current of an air flow and through different structures. These are intended to increase the transition time of the water between the top and bottom of the tower, thus promoting the extraction of more heat. The cooled water is then returned to the system to extract heat again.

However, the design of these equipments causes the dispersion of microparticles of water outside the system. Their quantity is more or less important depending on the condition and maintenance of the equipment. Unfortunately, a second consequence of this design is that it promotes the growth of microorganisms, some of which, such as Legionella pneumophila, pose a significant risk to the population that may be exposed to microorganism-laden microdroplets. In the population at risk, infection with this microorganism, leading to the development of the severe form of the legionnaire disease, is associated with a mortality rate between 10-15%. Following the outbreak of Legionelle in Quebec in 2012, the rules surrounding the management of these facilities have been strengthened. In Quebec, for example, all CTs must be registered and have a prevention program. Water analysis should be performed every 30 days, as well as before the equipment is put into operation after overwintering. The health risk is set at 10,000 UFC/L while the threshold for intervention is 1,000,000 UFC/L. In the first case, a primary disinfection must be carried out and in the second case the cooling tower must be completely stopped and disinfected.