Legionella testing under the Drinking Water Ordinance (Trinkwasserverordnung): obligations for landlords and WEG

Legionella bacteria multiply in hot water pipes when the water stands for too long or is not hot enough. They become dangerous when inhaled, for example in the shower. The 2023 Drinking Water Ordinance (Trinkwasserverordnung) therefore requires regular testing for many blocks of flats.

When the testing obligation applies

Under § 31 TrinkwV, drinking water must be tested for legionella if all of the following apply:

• The water is supplied as part of a commercial or public activity. Under § 2 TrinkwV, letting counts as a commercial activity.
• There is central water heating with a storage tank or instantaneous heater of more than 400 litres, or at least one pipe between the heater and the tap contains more than 3 litres (excluding the circulation pipe).
• The building has showers or other facilities in which water is atomised.
• It is not a one- or two-family house.

In rented residential buildings, testing must be carried out at least every three years. Samples are taken at several representative points, and the system needs suitable sampling valves for this. Only an approved testing laboratory may carry out the tests.

In a condominium, the central hot water system is part of the common property. In practice, the property manager therefore commissions the testing on behalf of the owners' association and keeps track of the date of the next test.

If the action value is reached

The technical action value is 100 colony-forming units per 100 millilitres (Anlage 3 Teil II TrinkwV). If it is reached, the testing laboratory reports this to the local public health office (Gesundheitsamt). Under § 51 TrinkwV, the operator must have the causes investigated without delay, including a site inspection and a check against the generally accepted rules of technology. The operator must prepare a written risk assessment and implement the necessary measures. The public health office must be informed of the measures, and the documentation must be kept for ten years.

Residents must be informed without delay as soon as the result of the risk assessment and any restrictions on the use of the water are available (§ 52 Abs. 3 TrinkwV). A ready-prepared notice template saves time in this situation.