Legionella in drinking water is no trivial matter: it can cause life-threatening Legionnaires' disease – and German law puts landlords and condo associations firmly on duty.
"The operator of a drinking water installation containing a large system for drinking water heating must have the water tested for Legionella spec. where the water is supplied in the course of a commercial activity."
— § 31 German Drinking Water Ordinance 2023 (translated)
Who must test
Rented multi-family buildings with a large system: a central hot-water tank over 400 litres or more than 3 litres of pipe volume between heater and the farthest tap. Letting counts as "commercial activity" – even for a small association with a single rented flat.
Intervals and threshold
- Testing every three years by an accredited laboratory.
- Sampling at representative points (flow, return, distant risers) by trained personnel.
- Technical action value: 100 CFU/100 ml.
If the threshold is exceeded
Immediately: notify the health authority, commission a risk analysis, inform residents, and take measures from thermal disinfection (flushing above 70 °C) up to shower bans. Routine testing costs are recoverable as hot-water costs; remediation is the owner's expense.
Manager's practice: run test dates as recurring tasks with document storage – the lab report belongs in the audit-proof property record.