Owners of a water supply facility (including private water supply) are required to have the water tested according to §14 of the Drinking Water Ordinance 2001. Examinations including sampling may only be carried out by authorized (accredited) testing laboratories.

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.

Legionella naturally occur in ground and surface water and thrive best in water at temperatures between 25-45°C. When ingested orally, Legionella are harmless. However, the inhalation of water contaminated with Legionella via the respiratory tract (aerosol formation, steam, showers, air conditioning, etc.) can cause a Legionella infection. Symptoms range from flu-like illness to fatal pneumonia.  
The Drinking Water Ordinance (TrinkwV 2001) contains a technical action level. The obligation for sampling is regulated by §14 para. 3 in conjunction with Annex 4 Part II of the Drinking Water Ordinance.

According to the requirements of the Drinking Water Ordinance (TrinkwV 2001), water used in a company for the production, processing, preservation or placement on the market of food must meet the general requirements for drinking water. The company owner must ensure that there is no adverse effect on the water in the company's pipeline network. Regulation (EC) No. 852/2004 also requires water of drinking water quality when used as an ingredient and for cleaning and disinfection.