Legionella species

Legionella species in domestic drinking water installations: Obligatory for home owners and building managers

The Drinking Water Ordinance (TrinkwV) engages owners and operators of larger water heating systems to have their systems tested for Legionella species. A violation of the requirements from the TrinkwV can have serious consequences for hirers and property managers, for example by punishment with a monetary fine of up to  € 25,000 or imprisonment of up to 2 years.
The first preliminary analysis had to be available by December 31, 2013. The TrinkwV stipulates that commercial properties must be tested for Legionella at least every three years.                                                                         
Legionella tests may only be carried out by laboratories that are accredited according to DIN EN ISO/IEC 17025. This requirement also includes sampling.

Who is subject to monitoring?

Mandatory monitoring applies to apartment buildings with more than two residential units and a central hot water supply (large systems). These objects must contain showers or other systems that result in nebulization of water and supply drinking water as part of a commercial or public operation. Large systems are systems with a storage volume > 400 L and/or a pipeline volume of ≧ 3 L, calculated from the outlet of the drinking water heater to the most distant point of use. The circulation return line is not taken into account.

What are Legionella species?

Legionella species are a genus of Gram-negative, nonspore-forming aerobic bacteria encompassing more than 50 species, which in turn comprise 70 different serogroups. All Legionella species can be classified as potential human pathogens. The most significant species for human diseases is Legionella pneumophila, which is the cause for about 90% of all Legionella-related diseases. Fourteen serogroups are known for Legionella pneumophila, of which serogroup 1 has the most clinical significance. Legionella diseases occur in two different forms, both of which can include symptoms such as malaise, fever, headache, aching limbs, chest pain, cough, diarrhea and confusion. The actual legionnaire’s disease is a form of severe pneumonia, which is fatal if left untreated in 5-10% of all cases. The incubation period is 2-10 days, in rare cases up to two weeks. The much more common Pontiac fever is a febrile, flu-like illness with an incubation period of up to two days and usually resolves within a few days without lung involvement.


The primary reservoir for Legionella species is fresh water. They are a natural part of the aquatic flora. The occurrence of Legionella species is decisively influenced by the water temperature; ideal growth conditions are water temperatures between 25 °C and 55 °C. Legionella species multiply intracellularly in amoebas and other protozoa that form biofilms in water conduit networks. This means that pipes, fittings, and air conditioning systems provide ideal conditions for the growth of Legionella species. In particular, there is often a drastic increase in the reproduction of Legionella species in the water of older and poorly maintained or rarely used hot water pipes and tanks.


Legionella species are mainly transmitted through inhalation of water droplets (aerosols) containing the bacteria. Possible sources of Legionella-containing aerosols are hot water systems found in

  • homes and apartments
  • swimming pools
  • showers and saunas
  • hospitals
  • senior care homes
  • hotels
  • schools
  • dormitories
  • sports facilities

as well as

  • air conditioners
  • dental practices
  • lawn sprinkler systems
  • cooling towers and ventilation systems with humidity control
  • wet separators

Infection can occur in the work-related as well as in the private spheres. Drinking contaminated water does not cause infections. A disease transmission from Person-to-person is not known to date.

Who is particularly at risk?

Older people, smokers and people with a weakened immune system or a chronic disease (e.g., diabetes) are particularly at risk. Men get sick more than twice as often as women.

What can we do for you?

We can assist you by providing accredited sampling, on-schedule results and professional advice.
We must immediately inform the public health authority if the technical threshold value is exceeded.

More information can be found in the Legionella flyer (PDF file). If we have sparked your interest, please request a detailed offer.