Legionella analysis; indication that the technical action value has been reached

Drinking water must be regularly tested for legionella. Not only public facilities are affected, but also landlords and landladies under certain conditions.

According to the Drinking Water Ordinance (TrinkwV), operators of a mobile water supply system, a building water supply system or a temporary water supply system must have the drinking water tested for legionella at several representative sampling points if it is supplied as part of a commercial or public activity, if

• there is a drinking water heating system with a storage drinking water heater or a central flow-through drinking water heater, each with a capacity of more than 400 liters, or a capacity of more than 3 liters in at least one drinking water pipe between the outlet of the drinking water heater and the tapping point for drinking water, whereby the content of a circulation pipe is not taken into account,
• there are showers or other facilities in the water supply system in which the drinking water is atomized, and
• the water supply system is not located in a detached or semi-detached house.

In the case of rentals, homeowners, landlords or communities of owners (possibly represented by a property management company) are deemed to be the operators of the water supply system.

In the case of commercial letting, the inspection must be carried out at least once every three years, and in the case of drinking water supply as part of a public activity, at least once a year. If no objections have been found during the annual inspections in three consecutive years, the public health department can also set longer inspection intervals of up to three years, provided that the system and mode of operation

• have not been changed and
• demonstrably comply with the generally recognized rules of technology.

The tests must be carried out in accordance with § 31 of the Drinking Water Ordinance (TrinkwV) and without being initiated by the public health department. The inspection intervals in accordance with § 31 Para. 2 TrinkwV apply:

• Installations (public activity): at least annually,
• Installations (commercial activity): at least every 3 years,
• Mobile water supply systems, e.g. on board land, water and air vehicles: the health authority determines the frequency,
• Temporary water supply systems, e.g. seasonally operated water supply systems in mountain huts: the health authority determines the frequency.

In the case of newly commissioned water supply systems, the first test must be carried out within three to twelve months of commissioning in accordance with Section 31 (4) TrinkwV.

A so-called technical measure value (TMW, value for triggering measures) of 100 CFU (colony-forming units) per 100 ml applies to contamination with legionella. When testing in accordance with Section 31 Para. 1, the testing body must immediately inform the operator of a water supply system if the TMW is reached in accordance with Section 39 Para. 4 No. 2 TrinkwV. In addition, this situation must be reported immediately to the responsible health authority in accordance with Section 53 (1) TrinkwV.

In addition, the operator of the water supply system (owner, property management) bears primary responsibility for the measures required under the Drinking Water Ordinance when the TMW is reached:

• The operator of a water supply system must immediately notify the public health department in accordance with Section 51 (1) No. 1 TrinkwV that the limit has been reached. The obligation to notify does not apply if the operator has proof that the notification has already been made by the testing body in accordance with Section 53 (1) TrinkwV.
• In accordance with Section 51 TrinkwV, the operator of a water supply system must immediately carry out investigations to clarify the causes, including a site inspection and an examination of compliance with the generally recognized rules of technology, or have such investigations carried out. In addition, they must prepare a risk assessment or have one prepared and implement measures that are necessary to protect the health of consumers. The health authority must be informed of the measures taken.
• The operator of a water supply system must immediately inform the affected consumers of the results of the risk assessment and any resulting restrictions on the use of drinking water.

In the case of extremely high legionella levels (over 10,000 CFU/100 ml), the showers may no longer be used until the problem has been eliminated. Use of the showers during this period is only possible if terminal bacteria-proof filters are installed.

• detailed laboratory findings need only be submitted on request