Evaporative cooling systems, cooling systems where water will be sprayed or otherwise may come into contact with the atmosphere. Evaporative cooling systems can, under certain conditions Legionella-containing water droplets (aerosols) emit, even leading by inhalation in humans to severe pneumonia resulting in death. The significance of the impact is not comparable example in environmental protection (Source: Federal Ministry for the Environment, Nature Conservation, and Nuclear Safety Construction / Ordinance on evaporative cooling systems, including natural draft cooling towers and wet scrubbers.). In Germany so far three major caused of appropriate equipment Legionella outbreaks have been documented. In January 2010, in Ulm / Neu-Ulm Legionella outbreak occurred with 65 patients and five dead; also in Warstein in August 2013 with 160 patients and two deaths. Another cluster with a total of 17 cases of disease was registered in July 2012 in room two bridges. Evaporative cooling systems have been identified as the main cause in all three cases as sources of infection. Ensuring proper and hygienic conditions in evaporative cooling equipment is sustainable only possible with oxygen-containing oxidation process.