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.

Fact Sheet on Legionella in Drinking Water

General Information and Origin

Legionella are environmental germs found worldwide. Naturally, they occur in small quantities in surface water and groundwater.

Especially in artificial water systems (e.g., water pipes in buildings), the pathogens find favorable growth conditions at certain temperatures. The multiplication of Legionella mainly occurs in sediments and deposits of the pipe system (biofilms). The presence of Legionella in artificial water systems is primarily influenced by the water temperature and the water's residence time. Especially poorly designed and inadequately maintained water systems are regularly affected by Legionella infestation.

Significance

Legionella cause various diseases in humans, such as flu-like symptoms or severe pneumonia, which can be fatal.

Legionellosis is primarily caused by inhaling atomized or aerosolized water. The pathogens spread through water droplets in the air and can thus be inhaled. Infection usually occurs through showers, whirlpools, humidifiers, faucets, or air conditioning systems. Human-to-human transmission is not possible.

Legal Regulations for Drinking Water

The Drinking Water Ordinance (TrinkwV 2001) prescribes regular testing for Legionella. This affects entrepreneurs and owners of drinking water installations with large systems for drinking water heating, if the water is commercially and/or publicly dispensed and there is also atomization of the water.

A large system refers to a storage drinking water heater or a central flow-through drinking water heater with a content of more than 400 liters or a content of more than three liters in at least one pipeline between the outlet of the drinking water heater and the withdrawal point.

The public dispensing concerns, for example, hospitals, schools, kindergartens, hotels, and nursing homes. These facilities are required to test for Legionella once a year. Likewise, owners/landlords of multi-family houses, housing associations, and property management companies are affected. For these, the required testing interval is three years.

The Drinking Water Ordinance stipulates a technical measure value of 100 colony-forming units (CFU) per 100 ml for Legionella. If this value is exceeded, it must be reported to the responsible health department.

If a company is not legally required to test for Legionella, an examination is still recommended as part of due diligence, especially if showers are present or there is contact with atomized or aerosolized water in other ways.

Important Causes for Elevated Germ Numbers

• Irregular use of water pipes
• Dead ends in the pipe system
• Insufficient regulator temperature on the drinking water heater
• Insufficient water temperatures in the pipe system

Growth Conditions

The optimal growth temperature for Legionella is between 25 - 45 °C.

At what temperatures do these microorganisms die?

At water temperatures above 55 °C, Legionella growth is inhibited. Above 60 °C, Legionella are generally killed.

To protect against Legionella infestation, the water should leave the hot water storage tank at a minimum of 60 °C and return to the storage tank at a minimum of 55 °C. The maximum temperature drop in the pipe system should not exceed five degrees. Water should also not stagnate in the pipes for more than 72 hours.

Further Information and Literature

• www.rki.de: under "Infectious Diseases A-Z"
• UBA recommendation "Systematic Testing of Drinking Water Installations for Legionella According to Drinking Water Ordinance - Sampling, Investigation Procedure, and Indication of Results" from December 18, 2018
• Drinking Water Ordinance - TrinkwV 2001
• www.umweltbundesamt.de under Topics: Drinking Water