Landlords or owners of large hot water systems in rented buildings must test the drinking water regularly for legionella bacteria. Operators of public buildings such as hospitals, swimming pools, gyms, hotels and retirement homes are also obliged to do so.

The obligation applies to buildings with at least three apartments in which hot water is supplied via a central large-scale plant. These plants either have a storage tank with a capacity of more than 400 litres or pipes with a water volume of more than 3 litres between the storage tank and the tap. Single-family and two-family houses are exempt from the inspection obligation.

If all apartments in a building are owner occupied, there is no obligation to have the water tested. However, if even one apartment is rented out and there is a large-scale hot waterplant, the drinking water must be tested.

No, if boilers are used in multi-story houses, there is no inspection obligation, even if the building has more than two apartments.

• In rented buildings with large-scale plants, the water must been tested for legionella at least every 3 years.
• In public buildings such as hospitals or swimming pools, it must been tested at least once a year.

The owner or landlord must commission an approved laboratory to test the water. You find a list of approved laboratories in Bremen here: List of approved laboratories for drinking water testing (pdf, 140.6 KB). The laboratory takes water samples on site and tests them.

Two samples must been taken from the hot water tank (flow and return flow) and additional samples in several apartments. The number of samples depends on the size of the building. The rule is: 3 samples are taken for every 10 rising pipes started. The water temperature is measured for each sample as well.

Yes, if the value of 100 CFU (= colony-forming units) of legionella per 100 ml of water is exceeded, the results must be reported to the health authority. Both the owner and the laboratory are obliged to do so.

The necessary measures taken depend on the concentration of legionella bacteria. For example, thermal disinfection may be required. This involves heating the water to at least 70°C. If the problem persists, parts of the system may need to be renovated. This is determined in a risk assessment, which the owner must have arranged.

Legionella bacteria spawn at temperatures between 25 and 55°C. At 60°C and above, they hardly multiply at all. So make sure that the hot water in the tank is always at least 60°C. Avoid letting water stand in the pipes for long periods, as this can pander the growth of legionella bacteria. If there are pipes that are not in use, they should be disconnected from the water supply.