Evaporative cooling systems release water droplets containing legionella under unfavorable conditions, which can lead to severe pneumonia in humans. To reduce this high risk potential, the VDI issued the guideline VDI 2047-2 in 2015, which regulates the hygiene requirements for the planning, construction, operation, and maintenance of such systems. The commentary on the implementation of these hygiene requirements comes from an authoritative source: the author was significantly involved in the development of VDI 2047-2. Taking into account the upcoming VDI 2047-3, all requirements are explained for the first time in a practical and step-by-step manner. Planners, builders, operators, manufacturers of evaporative cooling systems, and staff from supervisory authorities will be empowered by this title to apply the guideline confidently and in compliance with regulations.