At a glance
- Action level: 100 CFU/100 ml (technical action level, Annex 3 Part II TrinkwV)
- Testing interval: annually for public supply, every 3 years for commercial letting of residential property (§ 31 TrinkwV)
- Legal basis: testing obligation under § 31 TrinkwV 2023
- Sampling: only by an approved testing body accredited for Legionella (§ 39 TrinkwV)
- Retention: test results for at least 10 years (§ 44 TrinkwV)
Who is actually required to test?
The obligation applies when three conditions come together: a large-scale drinking water heating system (a tank of more than 400 litres, or more than 3 litres of water in the pipe between the heater and the point of use), points of use that create aerosols such as showers, and handing that water on commercially or to the public. For hotels, clinics and care homes, all three almost always apply.
Which Legionella testing intervals apply?
| Facility | Standard interval | Note |
|---|---|---|
| Hotel, accommodation | annually | public supply |
| Hospital, clinic | annually | increased risk of infection |
| Care and senior facility | annually | public supply |
| Letting of residential property | every 3 years | purely commercial supply |
| After 3 years without objection | extension possible | on application to the public health authority |
| After the action level is exceeded | as ordered | the public health authority decides |
These intervals are the standard case. After three consecutive years without any objection, the public health authority can extend the annual interval to up to three years. After an exceedance, a remediation or a longer operational interruption, however, it will order additional follow-up tests.
What happens if the action level is exceeded?
The technical action level is 100 CFU/100 ml. If it is exceeded, you are required to notify the public health authority without delay, to arrange a risk assessment by a qualified expert and to implement measures. From 10,000 CFU/100 ml there is imminent danger: immediate measures up to a shower ban are then possible.
How a finding should be classified depends on the measured concentration. The following classification summarises what action is required from which value:
Action level reached. No further measures are legally required.
Action level exceeded: notification to the public health authority, risk assessment and follow-up testing required.
Immediate risk assessment and remediation. A usage restriction should be considered.
Imminent danger: immediate measures up to a shower ban.
Classification based on the Umweltbundesamt (UBA), recommendation on the systemic testing for Legionella, and the Drinking Water Ordinance (§ 31 TrinkwV). Own illustration.
What testing does not replace
A sample is a snapshot at a few points of use. It says nothing about whether water was regularly exchanged in the meantime. That is exactly what regular flushing requires, and exactly what you must be able to prove during a test.
How long and how often flushing is required