Legionella is not a minor problem in industrial facilities. In 2020, 8,372 confirmed cases were reported across 27 EU/EEA countries, with 72% concentrated in Italy, France, Spain, and Germany. Yet many facility managers at industrial plants continue to view it as a “hospital” or “hotel” risk. This is a mistake with significant consequences.
Industrial systems—cooling towers, air conditioning systems, and domestic hot water systems with storage tanks—create exactly the ideal conditions for the bacteria: lukewarm water, stagnant water, and biofilms on internal surfaces. In industrial systems, the number of people exposed is often significant, and the operational consequences of contamination are immediate: emergency decontamination, partial or total shutdown of the facility, and reputational damage.
Regulations don’t wait: In 2023, Legislative Decree 18/2023 transposed EU Directive 2020/2184 on the safety of water intended for human consumption. In 2025, Legislative Decree 102/2025 further tightened the requirements for monitoring, inspection, and documentation. It is no longer optional. It is now mandated by law and enforceable.
When the bacterium * Legionella * becomes a problem in industrial facilities
The bacterium * Legionella * thrives under very specific conditions:
- Temperature: between 25°C and 45°C (maximum growth at 37°C)
- Stagnation: water that remains still for hours or days
- Biofilm: a biological film that protects bacteria from disinfectants
- Materials: Corroded or scaled pipes and tanks
In industrial facilities, these factors often coincide:
- Evaporative cooling towers: Water circulates at moderate temperatures, and the collection tanks accumulate sediment and biofilm.
- Storage-type domestic hot water systems: The water heater maintains the water at a nominal temperature of 60°C, but rarely used secondary pipes (“dead ends”) can cool down to 30–40°C, creating high-risk areas.
- Air conditioning and air handling systems (AHU): Condensate pans and evaporative circuits are ideal microenvironments for microbial growth.
- Wastewater treatment or biological treatment plants: aeration tanks, settling tanks, and systems where the water temperature exceeds 20°C and generates spray or aerosols.
The most significant consequence is not only operational but also administrative: the presence of Legionella requires immediate remediation, documentation, notification to local authorities, and potential liability for the operators.
The Role of Biofilm: The Invisible Enemy
A biofilm is an invisible biological film that adheres to the inner walls of pipes and tanks. It is not dirt, but a community of microorganisms bound together by a matrix of organic substances.
What makes biofilm dangerous?
- Protection against disinfectants: A standard disinfectant penetrates only the outer layers. The interior remains intact and continues to harbor bacteria.
- Gradual release: The biofilm breaks off in pieces from the walls, releasing Legionella directly into the network.
- Accumulation over time: if left untreated, it grows and thickens, making the situation worse.
For this reason, approaches based solely on periodic thermal shocks or occasional hyperchlorination have high failure rates. They address the symptom, not the cause.
The Law: What Legislative Decree 102/2025 Actually Says
Legislative Decree No. 102/2025 established clear requirements for high-risk facilities:
- Risk Assessment: Every facility with water, air conditioning, or cooling systems must conduct a technical and hygienic risk assessment Legionella.
- Monitoring: Facilities classified as medium-to-high risk must be sampled regularly (at least once a year for small facilities; every six months or more frequently for complex facilities).
- Action thresholds: The presence of Legionella requires immediate remediation and notification to the local health authority.
- Documentation: maintenance log, sampling reports, self-inspection protocols.
Responsibility lies with operators, owners, and facility managers and cannot be delegated. For industrial facilities with employees, the situation is even more sensitive: it falls under workplace safety obligations (Legislative Decree 81/2008), which imposes administrative and operational responsibilities in addition to legal ones.
Prevention Strategies: An Integrated Approach
Legionella 's prevention is not a single action. It is an integrated approach that combines design, thermal management, maintenance, and treatment. This approach consists of the following steps:
- Plant Design and Configuration
- Temperature Management
- Preventive Maintenance
- Continuous Water Treatment
The advantage of this approach: no biological buildup, no biofilm accumulation, and continuous compliance.
Monitoring: From Microbiological Analysis to Control
- Microbiological analysis: culture on selective media (reference method). Minimum annual frequency for small facilities; semiannual or quarterly for complex facilities. PCR is useful as a rapid screening tool, but culture-based confirmation remains the gold standard.
- Monitoring Disinfectant Residues: If you use chlorine or hydrogen peroxide, monitor the residue weekly (using colorimetric test strips or specific test kits).
- Cleaning of critical fixtures: showers, showerheads, and jet breakers accumulate biofilm. Perform a visual inspection monthly; replace them every six months.
- Maintenance log: Every service call must be documented. Not for bureaucratic reasons, but because the log serves as proof of due diligence if a problem arises.
Regulatory Compliance as an Operational Priority
Legionella contamination at an industrial facility results in:
- Emergency Remediation and Corrective Actions
- Partial or total shutdown of the plant
- Epidemiological Analysis and Contact Tracing
- Legal and Administrative Liability
A continuous prevention strategy ensures business continuity and regulatory compliance, while eliminating administrative risks.
Conclusion
Legionella bacteria in industrial facilities is not an emergency that should be handled haphazardly. It is a risk that can be managed systematically.
The water flowing invisibly through the pipes of an industrial plant is just as critical as the production process itself. Regulatory compliance depends on what happens inside the pipes, not on external appearances. Risk assessment, careful design, controlled temperatures, regular maintenance, and continuous treatment significantly reduce risk and ensure regulatory compliance.
Legislative Decree 102/2025 is not a threat. It is the framework that legitimizes investment in prevention and protects those who take it seriously. If you manage an industrial facility with water systems, a technical risk assessment Legionella today eliminates surprises tomorrow and ensures operational continuity.