What are Legionella?

Legionella are gram-nega­tive, aerobic bacteria that occur natu­rally in small numbers in non-salt surface waters and soil. Under certain condi­tions, Legionella can multiply in water-carrying pipes and fixtures. The optimal temper­a­tures for this are between 25°C and 45°C.

Legionella are clas­si­fied as poten­tially path­o­genic to humans; inhala­tion or microaspi­ra­tion of water droplets containing Legionella can cause Legion­naires’ disease, a form of pneu­monia, or Pontiac fever in humans.

Regular testing for Legionella is manda­tory for certain drinking water instal­la­tions systems according to the currently valid German drinking water regu­la­tion (TrinkwV [1]) as part of health protection.

Who is obligated to have Legionella testing conducted?

According to the currently valid German drinking water regu­la­tion (TrinkwV), busi­ness owners and other oper­a­tors of a water supply system are required to have the drinking water tested for Legionella as part of a systemic exam­i­na­tion in build­ings if the drinking water is dispensed as part of a commer­cial or public activity, if a large drinking water heating system is present, and if the water supply system contains showers or other facil­i­ties that result in the atom­iza­tion of the drinking water.

A large drinking water heating system is present if the drinking water heater has a storage volume of more than 400 liters or if there is a pipeline with a capacity of more than 3 liters between the outlet of the drinking water heater and the point of withdrawal.

Note: Oblig­a­tions for Legionella testing may also arise from other legal areas besides the German drinking water regulation.

When must a legionella analysis be carried out?

If the drinking water is supplied as part of a public activity, the systemic tests for legionella must be carried out annually

The health depart­ment can extend the interval up to three years under certain conditions.

If the drinking water is supplied as part of a commer­cial activity, but not a public activity, the systemic exam­i­na­tions for legionella must be carried out at least every three years.

If one of the above-mentioned systems is put into oper­a­tion for the first time, a legionella exam­i­na­tion must be carried out within 3 – 12 months after commis­sioning in accor­dance with § 14b para. 6 TrinkwV [1].

Which tapping points are important?

According to the currently valid Drinking Water Ordi­nance [1], samples must be taken at several repre­sen­ta­tive and suit­able sampling points as part of a systemic legionella exam­i­na­tion in accor­dance with the recom­men­da­tion of the Federal Envi­ron­ment Agency dated December 18, 2018 [2]. Samples are to be taken at the drinking water inlet and outlet of the drinking water heater as well as in the periphery to detect each riser.

What happens in case of a positive result?

If the tech­nical action value of 100 CFU per 100 milli­liters is exceeded in the course of a systemic exam­i­na­tion for Legionella, the labo­ra­tory is oblig­ated according to the currently valid Drinking Water Ordi­nance [1] to inform the respon­sible oper­ator as well as the respon­sible health authority.

Who is allowed to take samples for a legionella analysis?

Drinking water samples must be taken as part of an analysis for legionella in accor­dance with the Drinking Water Ordi­nance [1] by testing labo­ra­to­ries accred­ited for this purpose and approved in accor­dance with § 15 Para.4 Drinking Water Ordi­nance [1].


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