An examination for legionella in drinking water installations is required when all of the following points are met:

• Presence of a large system for drinking water heating (= flow-through water heater with a content of more than 400 liters or more than three liters in at least one pipeline between the outlet of the water heater and the extraction point)
• The drinking water is supplied through a commercial (e.g. rental) or public activity (e.g. schools, hospitals, nursing homes)
• Atomization of the drinking water

In these cases, a systemic examination must be conducted. The obligation to conduct the examination always lies with the operator and other owners of the water supply system.